The Offering Discovery Protocol

Introduction Automated Agents need a deterministic way to learn what a Service offers before selecting an enrollment, payment, fulfillment, or other downstream protocol. Human-oriented pages and private catalog interfaces do not provide a common discovery contract. A single rigid product model is also insufficient for domains as different as flights, downloadable materials, subscriptions, physical goods, and rented compute capacity. ODP provides a stable discovery envelope and lets each Service describe domain-specific data with machine-readable schemas. Discovery begins with the Service document at /.well-known/odp and continues through a fixed set of operations advertised by that document. ODP representations use JSON as defined by and HTTP semantics as defined by . A directory can help an Agent locate candidate Services. A directory indexes Service metadata, not complete Offering catalogs. The Agent queries each candidate Service for authoritative Collection and Offering data.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Scope ODP defines: discovery of a Service's ODP capabilities through a well-known Service document; deterministic navigation and search of Collections and Offerings; stable descriptive envelopes for Services, Collections, and Offerings; Service-defined structured Offering attributes described by JSON Schema; discovery of deterministic search terms, filters, and pagination capabilities; terse representations for result sets and full representations for inspection; optional links from discovery resources to browser experiences and subsequent operations; optional discovery of remote Model Context Protocol endpoints; and Agent and Service conformance requirements. ODP is applicable whether access is public or subject to authentication, enrollment, payment, or another policy enforced by the Service.

Non-Goals ODP does not define: a universal taxonomy or rigid domain model for products and services; a protocol for enrollment, authentication, payment, checkout, tax calculation, shipping, pickup, fulfillment, or delivery; MCP transport, capability, tool, resource, prompt, version-negotiation, or authorization behavior; a requirement to replicate a Service's full catalog into a directory; ranking policy, recommendation policy, or natural-language interpretation; a directory protocol or a requirement that a directory exist; or the business rules that determine whether an Offering can be acquired. Examples and domain profiles can demonstrate compute, flight, digital, physical, or other data. Those examples do not add requirements to the ODP core protocol.

Terminology

Agent: Software acting for a user or another principal that discovers and evaluates ODP resources.
Service: An origin that publishes an ODP Service document and exposes one or more ODP capabilities. A Service can represent a merchant, marketplace, public organization, software system, or another discoverable entity. A Service is not necessarily a seller.
Service Document: The JSON representation published at /.well-known/odp. It describes the Service and advertises the ODP operations that the Service exposes.
Collection: An optional, Service-defined grouping used to navigate or constrain Offerings. Collections can be hierarchical, overlapping, or independent and do not impose a universal taxonomy.
Offering: A discoverable description of something the Service makes available. An Offering can describe a free or paid item, a physical or digital good, a scheduled resource, a subscription, a rental, or another Service-defined opportunity.
Terse Representation: A partial Collection or Offering representation used for listing, search, navigation, and comparison. It uses the same field names and locations as the Full Representation.
Full Representation: A resource representation containing the complete ODP description available to the Agent under the current access policy.
Detail Fields: An optional, exhaustive list of fields present in the corresponding Full Representation and omitted from a Terse Representation. Entries are JSON Pointers.
Attribute Schema: A JSON Schema document that describes Service-defined structured data carried by an Offering.
Filter Definition: Metadata that describes a deterministic constraint accepted by a search or listing operation. Filter definitions use short Service-local identifiers and can be embedded or linked and paginated.
Service Origin: The canonical ASCII serialization of the origin from which the Service Document was retrieved. The Service Origin identifies the Service.
Local Resource Identifier: A Service-created and Service-managed string that identifies a Collection or Offering within one resource-type namespace at that Service.
Resource Identity: The tuple of Service Origin, resource type, and Local Resource Identifier. An Agent composes this tuple; a Service emits the Local Resource Identifier in the resource representation.
Resource Reference: An origin-relative absolute-path reference or an absolute URL that locates a browser representation, schema, subsequent operation, or other referenced resource. A Resource Reference does not define Resource Identity.
MCP Endpoint: A remote Model Context Protocol Streamable HTTP connection target advertised by a Service. An MCP Endpoint is not a browser link, ODP operation, or ODP Action.
Top-Level Document: The outermost JSON object carried by one ODP request or response body. Objects nested within that object, including terse result items, are not Top-Level Documents.
Subsequent Operation: An operation linked from an ODP resource whose semantics can be defined by ODP, AEP, MPP, x402, or another protocol.

Roles

Agent Role An Agent consumes Service Documents and advertised ODP resources. It selects advertised operations, constructs their fixed paths from http.endpoint_base, interprets Service-defined attributes using the applicable Attribute Schema, and honors live HTTP authentication and payment challenges. An Agent MUST NOT assume that an unadvertised ODP operation exists. An Agent MUST construct only the fixed paths defined by this document. An Agent MUST treat content received from a directory as discovery metadata rather than authoritative Offering data.

Service Role A Service publishes its Service Document and serves the ODP operations it advertises. The Service is authoritative for its Collections, Offerings, Attribute Schemas, filters, access policy, and subsequent-operation links. A Service MUST NOT advertise an ODP operation that it does not support. A Service MUST keep operation metadata consistent with the behavior available to the Agent under the applicable access policy.

Directory Relationship A directory is not an ODP protocol role. It is an optional discovery facility that helps an Agent find Services by indexing public Service metadata. A directory can cache Service documents subject to its own refresh policy, but it is not authoritative for Service-owned catalog data. This document defines no directory query, suggestion, filter, facet, count, ranking, or response wire format. A directory can index localized Service name, description, and keywords values and combine them with directory-owned signals. Those behaviors belong to the directory implementation and do not become ODP operations or ODP conformance requirements. Directory suggestions and facets describe the directory's Service index. Offering-search refinements describe candidate values for effective Service-owned Filter Definitions. An Agent MUST NOT treat either one as the other, and MUST retrieve the current Service Document and catalog data from a selected Service before treating them as authoritative. ODP conformance does not depend on the use, availability, or implementation of a directory.

Resource Identity and References

Service Identity The Service Origin identifies a Service. An Agent MUST derive it from the final Service Document response URL using the ASCII serialization algorithm in . The canonical serialization MUST use a lowercase scheme and host, MUST omit the default port, and MUST contain no path, query, fragment, or user information. The Service Origin scheme MUST be https. For local development, http is permitted only when the host is syntactically exactly localhost, 127.0.0.1, or [::1]. Resolving another host name to a loopback address does not qualify. A Service Document MUST NOT declare another value as the Service's identity. Control of the Service Origin is established through the origin and transport security rather than a self-asserted global identifier. Changing the Service Origin changes the Service identity.

Local Resource Identifiers Every Collection and Offering representation MUST contain id, a Local Resource Identifier created and managed by the Service. ODP does not prescribe the Service's identifier-generation algorithm. A Local Resource Identifier MUST contain between 1 and 128 ASCII characters. Every character MUST be an ASCII letter, decimal digit, hyphen (-), period (.), underscore (_), or tilde (~). The complete identifier MUST NOT be . or ... A Service MUST keep the identifier stable for the resource's lifetime and MUST NOT assign it to another resource in the same resource-type namespace. Services SHOULD use UUIDs where practical. A Service whose internal identifier does not satisfy this syntax MUST map it to a stable public ODP identifier. Collections and Offerings have separate identifier namespaces. The same Local Resource Identifier MAY identify one Collection and one Offering at a Service. It MUST NOT identify two Collections or two Offerings at that Service. Agents MUST treat a Local Resource Identifier as opaque. Comparison is exact and case-sensitive. Agents MUST NOT trim, case fold, URL-decode, parse, or infer semantics from an identifier.

Complete Resource Identity The Resource Identity of a Collection or Offering is the tuple:

The resource type is collection or offering. Agent implementations SHOULD expose Resource Identity as a structured value. They SHOULD NOT create an externally visible concatenated form whose delimiters or escaping would constitute an additional identifier syntax. The Service is responsible for the Local Resource Identifier. The Agent is responsible for associating it with the Service Origin and resource type established by the representation context. The Service does not need to serialize the complete tuple in each representation. An Agent MUST compare all three tuple members when determining whether two representations identify the same resource. A Resource Reference, response URL, name, schema, or attribute change does not by itself change Resource Identity.

Resource References Fields defined as Resource References, including Service links, Collection and Offering web_url, image src, and subsequent-operation href values, MUST contain one of: an origin-relative absolute-path reference beginning with exactly one /, resolved against the Service Origin according to ; or an absolute URL using the lowercase https scheme. For local development, an absolute URL MAY use the lowercase http scheme only with a host syntactically equal to localhost, 127.0.0.1, or [::1]. Path-relative references, parent-relative references, scheme-relative references, fragments, and user information are prohibited. A same-origin reference SHOULD use the origin-relative form. A cross-origin reference MUST use an absolute URL. Non-ASCII URL components MUST be percent-encoded before serialization. An Agent MUST resolve an origin-relative Resource Reference against the Service Origin, not against the path of the representation containing it. Following a cross-origin reference does not change the Service Origin or Resource Identity of the referring ODP resource. An Agent MUST apply origin and credential policy independently to the resolved target as required by the Security Considerations.

Versioning and Compatibility

Version Syntax Every Top-Level Document MUST contain odp_version. Its value is a JSON string in MAJOR.MINOR form. MAJOR and MINOR are unsigned decimal integers without leading zeroes except for the value 0. The protocol version defined by this document is 1.0. Nested objects MUST NOT repeat odp_version unless a specification explicitly defines the nested object as an independently processable Top-Level Document. Terse items in a list or search response inherit the version of their containing Top-Level Document.

Compatibility Rules An implementation MUST reject a Top-Level Document whose odp_version it does not support. The version defined by this document is exactly 1.0; support for another version is defined by the document that specifies that version. Each request and response Top-Level Document declares the version governing that document. The version is not inherited across HTTP exchanges.

HTTP Media Types and Negotiation

ODP JSON Media Type The media type for ODP request and response documents is application/odp+json and uses the JSON structured syntax suffix defined by . The media type has no required or optional parameters. Parameters do not select or modify the ODP protocol version. The odp_version member is the sole protocol-version authority. An Agent SHOULD send Accept: application/odp+json when requesting an ODP resource. A Service MAY return an ODP representation when Accept is absent, includes the wildcard media range, or permits application/odp+json. If the request's Accept field excludes application/odp+json, the Service MUST respond with 406 Not Acceptable. A request carrying an ODP Top-Level Document MUST use a Content-Type whose media-type essence is application/odp+json. A Service MUST respond with 415 Unsupported Media Type when a request body intended for an ODP operation has a missing, malformed, or different media type. A successful response carrying an ODP Top-Level Document MUST use a Content-Type whose media-type essence is application/odp+json. An Agent MUST reject a successful ODP response with a missing, malformed, or different media type. Media-type essence comparison is case-insensitive. Receivers MUST ignore syntactically valid media type parameters and MUST NOT interpret a version parameter or any other parameter as an ODP version declaration. HTTP Problem Details responses use application/problem+json. Attribute Schema documents use application/schema+json.

No Separate Version Negotiation Implementations MUST NOT negotiate the ODP version through a media-type parameter or a separate ODP version header. An Agent determines whether it can process a received Top-Level Document from odp_version and the compatibility rules in this document.

Discovery Architecture

Service Discovery An Agent can begin with a known Service origin or obtain candidate Service origins from a directory or another source. When a directory is used, the result of the first stage is a set of candidate Services. The result is not a cross-Service Offering search result.

Service Inspection An Agent retrieves the Service Document from /.well-known/odp at the Service origin. The Service Document advertises the ODP operations available to the Agent. The Agent constructs only advertised operations using the endpoint rules in this document.

Service Document

Retrieval and Access The Service Document is the response to GET /.well-known/odp. This request MUST be available without enrollment, authentication, or payment. A Service can enforce access policy on catalog operations advertised by the document. The successful response MUST be an ODP JSON Top-Level Document. The Service Document MUST be a flat JSON object and MUST contain odp_version, name, description, language, localizations, operations, and http. It MAY contain branding, documentation_url, keywords, mcp, payment_origins, protocols, search_capabilities, status_url, support_url, and website_url. It MUST NOT contain a self-asserted Service identifier or web_url. name is a non-empty string of at most 128 Unicode code points. description is a non-empty string of at most 1024 Unicode code points. keywords is an array of at most 32 unique freeform strings, each containing 1 through 64 Unicode code points and collectively containing at most 1024 Unicode code points. A keyword MUST begin and end with a non-whitespace code point. A Service SHOULD omit keywords when it has none. Keywords are localized Service-discovery hints in the language identified by language. They do not draw from a protocol-defined vocabulary, advertise accepted query terms, enumerate a catalog, or define filters. ODP defines no case folding, normalization, stemming, or semantic equivalence for them; array uniqueness uses JSON string equality. An Agent MUST NOT restrict a Collection or Offering search query to Service keywords or assume that a Service supports keyword enumeration or query completion.

Payment Origins payment_origins, when present, is a non-empty array of at most 16 Service Origins at which the Service can issue payment challenges. A Service omits payment_origins when it issues payment challenges only from its canonical Service Origin. Declaring an origin does not prove control of it; a directory can require independent verification before associating payments from that origin with the Service. A directory treats duplicate origins and the canonical Service Origin as redundant.

Service Links The Service Document MAY include the following Resource References: website_url identifies the human-facing Service website or storefront; documentation_url identifies human-readable documentation for using the Service; support_url identifies the Service's support destination; and status_url identifies the Service's operational status page. These links are descriptive metadata. Their presence does not advertise an ODP operation, alter an operation's access policy, or replace the machine-readable OpenAPI reference in http.openapi. website_url is not a base URL for other Resource References. In particular, a Collection or Offering web_url is resolved against the Service Origin. A Service whose browser resources use a different origin supplies an absolute URL in each applicable Resource Reference.

MCP Endpoints mcp, when present, is a non-empty array of remote MCP Endpoint descriptors. A Service with no MCP Endpoint omits mcp rather than serializing an empty array. Each descriptor MUST contain type and url and MAY contain name and description. type MUST be streamable-http, identifying the MCP Streamable HTTP transport . url is a Resource Reference to the remote MCP Endpoint. name, when present, is a non-empty human-readable label of no more than 128 Unicode code points. description, when present, is a non-empty explanation of the endpoint's purpose containing no more than 1024 Unicode code points. name and description use the Service Document's language and localization rules. An MCP descriptor locates a connection surface; it does not describe an individual MCP tool. A Service SHOULD use one descriptor for tools exposed through one MCP connection surface and SHOULD use multiple descriptors only for distinct connection surfaces. Array order has no protocol semantics. Retrieving, validating, or indexing a Service Document MUST NOT invoke an advertised MCP Endpoint. An MCP-capable client connects only when its caller's operation requires that interface. MCP remains authoritative for capability discovery, version negotiation, tools, resources, prompts, authorization, and request behavior. The presence of an MCP descriptor does not state that the endpoint is public and does not authorize an Agent to send ODP, AEP, payment, or other credentials.

Branding branding, when present, contains exactly icon and logo. Each member contains a required Resource Reference src and MAY contain a type of image/svg+xml, image/png, or image/webp. type is a media-type hint available before retrieval. A Service SHOULD provide it when the Resource Reference does not have a filename extension that identifies the image format. icon identifies a Service mark intended for a square presentation canvas. logo identifies a Service mark intended for a horizontal 4:1 presentation canvas. Services SHOULD provide sufficient source resolution to avoid upscaling. SVG resources MUST provide positive intrinsic dimensions or a positive view-box width and height. A client that normalizes branding for storage or presentation MUST preserve the source aspect ratio and MUST NOT crop or stretch the source. The client fits and centers icon within a square canvas and logo within a 4:1 canvas. Unused canvas pixels MUST be transparent when the normalized format supports transparency. The RECOMMENDED normalized dimensions are 200 by 200 pixels for icon and 400 by 100 pixels for logo. Branding retrieval is anonymous. A client MUST NOT attach AEP credentials, payment credentials, cookies, or authorization fields. When type is present, the successful response media-type essence MUST equal the advertised value. A branding response body is limited to 1,048,576 bytes and five redirects. Redirect and network-address policy follows Supporting Resource Retrieval. Branding content is untrusted input. A client that displays SVG MUST either sanitize and safely isolate it or render it to a non-active raster representation before display. protocols advertises Service-wide support for enrollment, payment, and trust protocols. It contains at least one of enrollment, payments, or trust. An unsupported category is omitted rather than serialized as an empty array. enrollment, when present, is the single-item array [{"name":"aep"}], identifying AEP . An enrollment descriptor contains only name. trust, when present, is the single-item array [{"name":"tap"}], identifying Visa Trusted Agent Protocol . A trust descriptor contains only name. Advertisement states that the Service accepts and verifies requests using the named trust protocol. It does not prove Service ownership, authorize disclosure of consumer information, or replace the trust protocol's request validation. payments, when present, is a non-empty array of no more than two payment descriptors. Each descriptor contains name and authentication and MAY contain options. name is mpp, identifying the Payment HTTP Authentication Scheme , or x402, identifying the x402 protocol . Names MUST NOT be duplicated. When both descriptors are present, their array order expresses Service preference. authentication is not-required or required and states whether the Agent must authenticate to the Service before using that payment protocol. A required value requires the Service Document to advertise an enrollment protocol. A Service MUST advertise only enrollment, payment, and trust protocol names defined by the ODP version declared by its Service Document. An Agent MUST filter descriptors whose name it does not recognize before applying the known category's item limit, uniqueness rules, and descriptor validation. A category containing no recognized descriptors after filtering is treated as absent. An unknown protocol name MUST NOT make an otherwise usable Service Document invalid. A descriptor bearing a recognized name remains subject to every requirement for that descriptor and is not made valid by filtering. options, when present, is a non-empty array of no more than 16 unique payment-option names drawn from algorand, aptos, arbitrum, avalanche, base, card, ethereum, hedera, inflow, lightning, polygon, solana, stellar, stripe, tempo, and ton. Each name is a compact, human-consumable compatibility label. It does not replace protocol-specific method, scheme, network, chain, asset, or settlement terms. A Service MUST advertise an option only under a payment protocol through which it accepts that option. Omitting options means that the Service advertises the payment protocol without advertising detailed option compatibility. Protocol advertisement describes support and the authentication prerequisite for each payment rail; it does not guarantee that a payment or trust protocol is accepted by every ODP operation, catalog resource, or Action. A missing category means only that support is not advertised. An Agent and directory MAY derive a Service-support summary from this field. Recognition of a protocol or option by ODP does not imply that an Agent implementation supports or is configured to use it. A live HTTP response remains authoritative for the request that produced it.

Language Selection language MUST be the language tag of the representation. localizations MUST be a non-empty array of no more than 16 unique RFC 5646 language tags available for the Service metadata. It MUST include language. These fields describe the Service Document metadata and do not assert which localizations are available for Collections or Offerings. An Agent requests a preferred representation using Accept-Language. A Service supporting multiple representations MUST select a language using the Lookup scheme in . If no requested range matches, it MUST return its default representation rather than 406 Not Acceptable. A localized response MUST include Content-Language and Vary: Accept-Language. Entity tags MUST distinguish representation variants. ODP does not define a language query parameter.

HTTP Endpoint Base http MUST be an object containing endpoint_base and MAY contain openapi. endpoint_base is an origin-relative absolute-path reference beginning with exactly one /, MUST NOT contain a query or fragment, and MUST contain no more than 2048 ASCII characters. The value MAY end in /. openapi, when present, contains exactly one member, url, whose value is a Resource Reference to a reusable OpenAPI 3.1 document. It supplies the default OpenAPI document for Actions whose OpenAPI target omits url. An Action-level url overrides this Service-wide value. Advertising openapi does not require an Action to use it and does not make OpenAPI a dependency of ODP navigation. An Agent constructs an operation URL by removing any trailing slash from endpoint_base, appending one /, and appending the fixed path from the following table. Identifier placeholders are replaced verbatim with valid Local Resource Identifiers; percent-encoding or decoding is not performed. Operation identifier Method Fixed path list-collections GET collections search-collections POST collections/search get-collection GET collections/{collection_id} list-collection-offerings GET collections/{collection_id}/offerings list-offerings GET offerings search-offerings POST offerings/search get-offering GET offerings/{offering_id} Query parameters can modify a request where an operation defines them. They are not part of Resource Identity and MUST NOT be used to carry Collection or Offering identifiers.

Representation Selection Every Collection and Offering operation supports the representation query parameter. Its value MUST be terse or full. An absent parameter selects the operation default in the following table. Operation identifier Default representation list-collections Terse items search-collections Terse items get-collection Full Collection list-collection-offerings Terse items list-offerings Terse items search-offerings Terse items get-offering Full Offering representation=terse selects Terse Representations and representation=full selects Full Representations regardless of the operation default. On a list or search operation, the selection applies to every Collection or Offering item in the response, not to the page envelope. A request MUST NOT contain more than one representation parameter. A Service MUST reject an unsupported or repeated value with 400 Bad Request. The query parameter does not change Resource Identity. HTTP caches distinguish query-target variants according to normal HTTP cache-key rules. Pagination and response limits apply independently of the selected representation. An Agent requesting Full Representations from a list or search operation MUST NOT assume that the Service will increase its page or response limits.

Operation Advertisement operations MUST be an array of no more than seven Operation Descriptors. Every descriptor MUST contain exactly name and authentication. name is an operation identifier from the preceding table and MUST be unique in the array. authentication is one of not-required, optional, or required: Value Meaning not-required The operation is usable without Service authentication. optional The operation is usable anonymously; authentication can expand content. required The operation requires Service authentication before it can succeed. An optional or required value requires the Service Document to advertise an enrollment protocol. optional does not require every anonymous response to differ from an authenticated response. It states that the operation supports both contexts and that authentication can affect the visible catalog content. An Agent MUST NOT invoke an ODP operation that the Service Document does not advertise. Every conformant Service MUST advertise and implement list-offerings and get-offering; consequently, the array contains at least two descriptors. The remaining operations are optional and are implemented only when advertised.

Processing Limits The decoded UTF-8 Service Document MUST NOT exceed 65,536 bytes or a JSON nesting depth of 8. String and array limits in this section are measured after JSON decoding. A Service MUST produce a document within every limit. An Agent MUST reject the entire document if a required member is missing, a limit is exceeded, or the document is otherwise invalid; it MUST NOT act on a partially parsed Service Document. An Agent MUST follow no more than five redirects while retrieving the Service Document. Every redirect target MUST have the same scheme, host, and effective port as the preceding request. The Agent MUST reject cross-origin redirects, transport-security downgrades, and redirect loops.

HTTP Caching HTTP cache directives and validators are authoritative. When a response supplies no freshness information, an SDK SHOULD use configurable fallback freshness lifetimes of four hours for Service Documents, one hour for Collections, five minutes for Offerings, zero seconds for search responses, one hour for Filter and Sort Definitions, and 24 hours for Attribute Schemas. Each resource class MUST be configurable independently. A fallback does not override Cache-Control, Expires, validators, or other HTTP caching semantics. An Agent cache MUST partition anonymous responses from responses obtained with Service authentication. It MUST NOT reuse an authenticated representation, page, schema, or capability document for an anonymous request or for a different authentication context. This requirement applies even when the URI and selected representation are identical.

Pagination

Page Envelope Every successful list or search response is an ODP Top-Level Document containing odp_version and items. items is an array and can be empty. A response containing another page MUST also contain next. The final page MUST omit next; an empty items array alone does not prove that the sequence ended. A page MAY contain auth_expands with the only valid value true. Its presence states that retrying the operation with acceptable Service authentication can expose additional items or additional fields in returned items under the current query. It does not identify, count, or describe protected content. A Service MUST omit the member rather than serialize false. next is a Resource Reference of no more than 2048 ASCII characters. It MUST resolve to the same origin as the initial operation. An Agent MUST preserve it exactly and MUST NOT decode, modify, construct, or derive behavior from its path, query, or embedded continuation token. ODP does not define previous-page traversal, numeric page indexes, offsets, or total-result counts. An Agent that needs to restart traversal repeats the initial operation request.

Continuation Requests An Agent retrieves next with GET. The response is another page envelope governed by the same representation and access context. Only omission of next marks the end of the sequence. A continuation response MUST advance traversal and MUST NOT return the request URL as its own next. The Service chooses the continuation URL and preserves every input needed to continue the original operation, including representation, filters, search terms, sorting, access context, and page-size policy. The Agent does not repeat the original request body or reconstruct those inputs. A continuation link from a POST search is still retrieved with GET. Every initial list and search operation accepts limit, an integer from 1 through 100 that requests the maximum number of items per page. GET operations carry it as a query parameter; POST search operations carry it as a top-level request-body member. A Service MAY return fewer items than requested. A Service chooses its default page size when limit is absent. An Agent-oriented SDK SHOULD use a configurable initial page size with a default of 50 and MAY request fewer items when its caller's remaining overall result limit is smaller.

Continuation Semantics A continuation sequence contains a stable logical sequence of Resource Identities and their order. Within one traversal, the Service MUST NOT change that sequence or return the same Resource Identity more than once. Resource representations can reflect changes made after the initial request, but membership and ordering in the continuation sequence remain stable. An item's id is the final deterministic ordering tie-breaker. Each next link MUST remain usable for at least one hour after issuance. A Service MAY choose a longer lifetime. An expired continuation MUST NOT silently restart traversal; the Service returns an expired-continuation problem, and an Agent-oriented SDK reports that failure to its caller. The continuation link is an interface contract, not a server storage model. Its path or query MAY contain a self-contained authenticated cursor or a reference to server-managed state. A stateless cursor can carry a query digest, snapshot or revision, keyset boundary, access-context binding, and expiration. Clients cannot distinguish stateless and stateful continuation and MUST treat both identically. A self-contained cursor embedded in next MUST be integrity protected. It MUST NOT disclose credentials, private catalog data, access-policy details, or other sensitive state. A Service SHOULD encrypt a self-contained cursor whose continuation state is confidential. A Service MUST validate every cursor as untrusted input and MUST NOT treat possession of a cursor as authorization.

Agent Iteration An Agent-oriented SDK SHOULD expose list and search results as asynchronous iterables that retrieve continuation pages automatically. Its ordinary item interface SHOULD yield Collection or Offering representations rather than page envelopes or continuation links. A lower-level page interface MAY expose items and next for callers that require explicit page control. An overall caller result limit is independent of the Service page limit. Reaching the caller's limit stops local iteration and does not imply that the Service sequence ended. An SDK MUST NOT fetch another page after the caller stops iteration.

Page Caching and Conditional Requests Each page request has its own HTTP cache key and validators under and . For GET pages, a Service SHOULD provide an entity tag and honor conditional retrieval such as If-None-Match; an unchanged conditional GET returns 304 Not Modified. Collection and Offering page fallbacks use their applicable resource-class freshness lifetime. Filter Definition pages use the Filter Definition fallback. Search responses, including their GET continuation pages, retain the zero-second fallback freshness lifetime. A POST search response is cacheable only when explicit HTTP semantics permit it. A continuation link does not override cache directives, create a shared-cache authorization, or make a private response public.

Catalog Discovery Collections are optional navigation resources. A Service can expose Offering search without Collections, Collection search without a hierarchy, or both. An Offering can belong to zero, one, or multiple Collections. List, search, and retrieval operations use the representation defaults and overrides defined in Representation Selection. An Agent obtains an individual Full Representation by applying the terse item's id to the applicable fixed retrieval operation.

Terse and Full Representations

Stable Field Placement A Terse Representation and its corresponding Full Representation describe the same Resource Identity. A field has the same name, location, type, and semantics in both representations. A Service MUST NOT move Service-defined attributes or core fields into a separate preview, summary, or representation-specific container. Every Terse Representation MUST contain id and name. Other fields are optional in a Terse Representation unless their resource contract requires them. A Service selects which optional fields to include according to the usefulness and cost of those fields. It MAY include every field from the Full Representation. A field present in both representations MUST have equivalent meaning; volatile values MAY differ because the representations were generated at different times. A Terse Representation omits fields or nested object members; it does not silently truncate an included scalar or array. An included object can omit members recursively. A field whose own contract explicitly defines truncation, pagination, or summary semantics follows that contract. A Full Representation MUST contain every ODP field available for that resource under the request's current access policy. This completeness requirement does not require inapplicable optional fields, fields withheld by access policy, or data that the Service does not possess. A Collection or Offering representation MAY contain auth_expands with the only valid value true. Its presence states that retrying its retrieval with acceptable Service authentication can expose additional fields for that resource. The member does not identify protected fields, promise access to a particular principal, or replace a live authentication challenge. A Service MUST omit the member rather than serialize false.

Detail Fields A Terse Representation MAY contain detail_fields. A Full Representation MUST NOT contain detail_fields. The value is a non-empty array of no more than 32 unique JSON Pointer strings as defined by . Each pointer MUST contain no more than 256 printable ASCII characters, MUST begin with /, and MUST NOT use the URI fragment representation of a JSON Pointer. Each pointer identifies a field present in the corresponding Full Representation and absent from the Terse Representation. A pointer to an omitted object or array covers its complete subtree. Top-level document metadata inherited by an embedded Terse Representation, including odp_version, is not a detail field. When detail_fields is present, it MUST exhaustively identify the minimal omitted field subtrees. When an exhaustive list would exceed a limit in this section, the Service MUST omit detail_fields instead of returning a partial list. Absence of detail_fields makes no claim about whether the Full Representation contains additional fields. detail_fields advertises only what an Agent obtains by retrieving the Full Representation. It does not advertise or enable field projection, grant access to the Full Representation, or override a live authentication or payment challenge. A Service MUST NOT disclose protected field existence through detail_fields when the current principal is not permitted to learn that information.

No Field Projection ODP version 1.0 does not define a request syntax for selecting arbitrary resource fields. An Agent MUST NOT infer field-projection support from detail_fields, an Attribute Schema, or an unknown query parameter. A future compatible revision can advertise and define projection independently. Collections and Offerings MAY include a web_url link for a human-facing browser experience. The browser representation is informative for Agent operation and does not replace the machine-readable ODP resource.

Resource Images A Collection or Offering MAY contain images, a non-empty ordered array of no more than 16 image descriptors. The first descriptor identifies the primary image. Each descriptor MUST contain src, a Resource Reference, and MAY contain alt, height, type, and width. Two descriptors in one array MUST NOT contain the same src value. alt, when present, is non-empty alternative text of no more than 1024 Unicode code points in the language of the containing representation. height and width, when present, are positive integer intrinsic dimensions in CSS pixels no greater than 65535. type, when present, is a media-type hint of image/avif, image/jpeg, image/png, image/svg+xml, or image/webp. A Terse Representation MAY include only the primary image even when the Full Representation contains additional images. This is the sole summary behavior of images; descriptors themselves MUST NOT be partially serialized. Omitting images from a Terse Representation makes no claim that the Full Representation has no images. Image retrieval is anonymous. A client MUST NOT attach AEP credentials, payment credentials, cookies, or caller authorization fields. The response Content-Type is authoritative. When an advertised type differs from the response media-type essence or the response is not a supported image type, a client rejects only that image. Image content is untrusted input and remains subject to the client's network, decoding, rendering, and resource limits.

Collections

Collection Search The search-collections operation accepts an ODP Top-Level Document containing odp_version and at least one of query or parent_id. It MAY also contain limit. A request containing neither search criterion is invalid; an Agent uses list-collections for an unconstrained sequence. query is a non-empty string of no more than 256 Unicode code points and MUST contain at least one non-whitespace character. It conveys text-search intent to the Service. The Service owns query interpretation, matching, indexing, and relevance. It can use lexical, full-text, language-aware, semantic, or other matching over Collection metadata visible under the request's access and language context. ODP does not define tokenization, stemming, case folding, searchable fields, or a portable relevance algorithm. An Agent MUST NOT assume that the same query produces equivalent matches at different Services. parent_id defines an exact hierarchy constraint. An omitted parent_id applies no hierarchy constraint. A JSON null value selects root Collections, which omit parent_ids. A Local Resource Identifier selects Collections whose parent_ids contains that identifier, meaning its direct children. It does not select the named Collection or recursively select descendants. When both query and parent_id are present, a Collection MUST satisfy both criteria. The parent_id predicate retains its exact protocol-defined meaning regardless of how the Service interprets query. The Service chooses result ordering. It can use relevance, curated taxonomy order, popularity, or another Service policy, and ODP version 1.0 defines no client-selected Collection sort. The common pagination contract requires the chosen logical sequence to remain stable during one traversal and uses id as the final ordering tie-breaker. An Agent MUST NOT reorder results before exposing them unless its caller explicitly requests local presentation ordering. The successful response is a page envelope containing Collection Representations selected by the common representation query parameter. No matches produce 200 OK with an empty items array. Malformed request bodies or unsupported member values produce an INVALID_REQUEST problem. The request and response use application/odp+json.

Collection Envelope A Full Collection Representation MUST contain odp_version, id, and name. It MAY contain description, images, language, localizations, parent_ids, web_url, and search_capabilities. Other Collection capabilities are defined by the operation or feature that uses them. An optional field with no applicable or available value is omitted rather than serialized as an empty value. language and localizations have the syntax and meaning defined for Service Document language metadata, but describe this Collection. They are omitted when the Collection uses the applicable language metadata inherited from its containing response or Service Document. Collection retrieval uses the same Accept-Language, Lookup, fallback, Content-Language, Vary, and entity-tag rules as Service Document retrieval. When present, parent_ids MUST be a non-empty array of unique Local Resource Identifiers. Every identifier names a direct parent Collection at the same Service. An omitted parent_ids identifies a root Collection. A Service can publish multiple roots or a flat set in which every Collection is a root. A Terse Collection follows the common Terse Representation contract. It MUST contain id and name; it can omit any other optional terse field, including parent_ids, and can use detail_fields to identify fields available through full retrieval.

Hierarchy Collection parent relationships form a directed acyclic graph. A Collection MAY have more than one parent. A Collection MUST NOT name itself as a parent, every parent identifier MUST resolve to a Collection visible under the same access context, and following parent relationships MUST NOT produce a cycle. The maximum path from a Collection through successive parents is 32 edges. A conforming Service MUST NOT publish a deeper hierarchy. Breadth and parent-array cardinality are governed by the common resource and response limits rather than the depth limit. parent_ids is the sole serialized source of hierarchy edges. Collections do not duplicate edges in a child_ids field. An Agent discovers direct children through Collection search constrained by the parent identifier. The Collection search contract defines that constraint. An Agent traversing hierarchy data MUST track visited Resource Identities. When an edge closes a cycle, exceeds the depth limit, names the current Collection, or names a missing Collection, the Agent MUST ignore that edge. The invalid edge does not invalidate unrelated Collections, hierarchy edges, Offering memberships, or operations.

Offering Membership When present, collection_ids MUST be a non-empty array of unique Local Resource Identifiers. Each identifier names a Collection at the same Service in which the Offering is a direct member. An omitted collection_ids means that the Offering has no Collection membership. A Terse Offering MAY omit collection_ids under the common Terse Representation rules. The list-collection-offerings operation is the inverse query over this relationship: it returns Offerings whose collection_ids contains the requested Collection identifier. A Service MUST keep the operation result consistent with the Offering membership it publishes. Hierarchy and membership are independent. Membership in a child Collection does not imply membership in any ancestor Collection. ODP version 1.0 does not define implicit descendant expansion. Offering search can request explicit descendant inclusion without changing direct membership semantics. Every collection_ids entry MUST resolve to a Collection visible under the same access context. An Agent MUST ignore a missing membership edge without rejecting the Offering or unrelated memberships.

No Synthetic Collection Identity ODP does not define an "All Offerings" Collection, reserve a Collection identifier for that purpose, or assign Resource Identity to a client-side convenience view. An Agent uses list-offerings for the complete accessible Offering sequence. A Service can publish an ordinary Collection with equivalent business meaning, and an SDK can label list-offerings for user-interface convenience without creating an ODP resource.

Offerings

Offering Search The search-offerings operation accepts an ODP Top-Level Document containing odp_version and at least one of query or filters. It MAY also contain collection_id, include_descendants, sort, refinements, and limit. An Agent uses list-offerings for an unconstrained sequence and list-collection-offerings for the unconstrained direct members of one Collection. query is a non-empty string of no more than 256 Unicode code points and MUST contain at least one non-whitespace character. It conveys text-search intent to the Service. The Service owns query interpretation, matching, indexing, and relevance. It can use lexical, full-text, language-aware, semantic, or other matching over Offering metadata and Service-defined attributes visible under the request's access and language context. ODP does not define tokenization, stemming, case folding, searchable fields, or a portable relevance algorithm. An Agent MUST NOT assume that the same query produces equivalent matches at different Services. filters and sort use the Filter Expression and Sort Definition contracts in this document. When query and filters are both present, an Offering MUST satisfy the Service-interpreted query and every Filter Expression. An omitted sort preserves the Service's preferred ordering. collection_id is a Local Resource Identifier that constrains results to Offerings in the named Collection. The Collection MUST resolve under the current access context. Otherwise, the Service returns 404 Not Found with a NOT_FOUND problem. A Service MAY use the same response when revealing that an inaccessible Collection exists would disclose protected information. include_descendants is a Boolean and MUST NOT appear without collection_id. Its default is false. When false or omitted, an Offering matches the Collection constraint only when its collection_ids contains collection_id. When true, an Offering matches when it is a direct member of the named Collection or any Collection reachable by following child relationships from it. This expansion does not alter or imply Offering membership. Descendant expansion observes the common Collection graph depth and invalid-edge rules. A Collection reachable through multiple paths is processed once. An Offering belonging to multiple included Collections appears at most once in the result sequence. The Service chooses result ordering. It can use relevance, curated ranking, popularity, or another Service policy, and ODP version 1.0 defines no client-selected Offering sort. The common pagination contract requires the chosen logical sequence to remain stable during one traversal and uses id as the final ordering tie-breaker. An Agent MUST NOT reorder results before exposing them unless its caller explicitly requests local presentation ordering. The successful response is a page envelope containing Offering Representations selected by the common representation query parameter. No matches produce 200 OK with an empty items array. Malformed request bodies or unsupported member values produce an INVALID_REQUEST problem. The request and response use application/odp+json. When requested, the initial response MAY also contain the bounded Refinement Groups defined below. A continuation response MUST omit refinements. Refinements describe the complete logical result set for the initial request, not only the Offerings serialized on its first page.

Offering Envelope A Full Offering Representation MUST contain odp_version, id, and name. It MAY contain description, images, language, localizations, web_url, collection_ids, price, schema, attributes, and actions. An optional field with no applicable or available value is omitted. In particular, a Service MUST NOT serialize empty attributes, collection_ids, or actions merely to declare that the capability is unused. language and localizations have the syntax and meaning defined for Service Document language metadata, but describe this Offering. They are omitted when the Offering uses the applicable language metadata inherited from its containing response or Service Document. A containing response can establish language metadata for its embedded items. The nearest metadata in the order Offering, containing response, then Service Document applies. Offering retrieval uses the same Accept-Language, Lookup, fallback, Content-Language, Vary, and entity-tag rules as Service Document retrieval. Content-Language identifies the language actually selected for the HTTP representation. A Terse Offering follows the common Terse Representation contract. It MUST contain id and name. It MAY include price and any other optional terse field except actions. Absence of web_url, price, schema, attributes, or another optional field from a Terse Offering makes no claim that the field is absent from the Full Offering. detail_fields can identify fields available through full retrieval.

Service-Defined Attributes and Schema attributes, when present, MUST be a non-empty JSON object containing Service-defined Offering data. An Offering that contains attributes MUST also contain schema. A Service MUST omit both fields when it has no Service-defined attributes for the Offering. schema identifies a JSON Schema Draft 2020-12 document that validates the complete attributes object. It contains exactly one member, url, a Resource Reference. Multiple Offerings MAY share one Attribute Schema. HTTP response metadata and the schema document itself describe the retrieved resource; the ODP reference does not repeat a media type, version, digest, or caching metadata. When a Terse Offering contains attributes, it MUST also contain schema. The Attribute Schema describes the complete Full Offering attributes. The recursively omitted members of terse attributes can be identified through detail_fields.

Attribute Schema Retrieval and Processing An Agent resolves schema.url against the Offering response URL and retrieves it with GET. It SHOULD send Accept: application/schema+json. A successful response MUST have a Content-Type whose media-type essence is application/schema+json and MUST contain a JSON Schema Draft 2020-12 document. A missing, malformed, differently typed, or invalid document is an unusable Attribute Schema. An Attribute Schema is an ordinary mutable HTTP resource. HTTP cache directives and validators are authoritative, and the Attribute Schema fallback defined in HTTP Caching applies when the response provides no freshness information. Neither the schema URL nor a previously retrieved schema makes the schema immutable. An Agent revalidates or refreshes it according to ordinary HTTP caching semantics. The schema MUST declare the Draft 2020-12 meta-schema through $schema. $id, when present, and references have their standard JSON Schema meanings subject to one interoperability restriction: the value of $dynamicRef MUST be a fragment-only URI-reference beginning with #. Cross-document references use $ref. An Attribute Schema containing a non-fragment $dynamicRef is unsupported. An Agent MUST process references needed to interpret or validate the instance. If the schema declares a required vocabulary the Agent does not support, the Attribute Schema is unsupported. Optional vocabularies and unknown keywords are handled according to JSON Schema Draft 2020-12. An Agent-oriented SDK SHOULD resolve and cache referenced schema resources and provide its caller a locally complete schema representation. The caller MUST NOT be required to perform additional network requests merely to interpret the returned Offering. Retrieval limits and protections apply to the complete reference graph rather than independently granting every reference unbounded network access. A Service MUST validate the complete attributes object in a Full Offering against its Attribute Schema. An Agent SHOULD validate Full Offering attributes before relying on them. Terse Offering attributes are a partial view of the Full Offering instance and MUST NOT be validated as though they were the complete instance. Every included terse value retains the type and meaning assigned by the Attribute Schema. An unavailable, invalid, unsupported, or non-matching Attribute Schema makes the Offering's attributes uninterpretable. It does not invalidate the Offering's identity, core descriptive fields, Price Preview, web_url, Collection membership, or actions. Agent-oriented SDKs SHOULD omit uninterpretable attributes from their normalized result and report a scoped issue separately. The SDK result shape is an implementation contract and does not add an issues member to the ODP wire representation.

Price Preview An Offering MAY contain price, a discovery-time summary that helps an Agent evaluate and compare Offerings before invoking a subsequent operation. Absence of price means that the Service has not advertised a price. It MUST NOT be interpreted as free. Every Price Preview contains a type discriminator. This specification defines free, fixed, range, starting_at, metered, and quote. Monetary values MUST be non-negative decimal strings and MUST NOT be represented as JSON numbers. currency is the display denomination of the summary; it does not select a payment protocol, network, rail, or settlement asset. Type Required members Meaning free type No price is required. fixed type, amount, currency One advertised display price. range type, minimum, maximum, currency An inclusive advertised display range. starting_at type, amount, currency The lowest advertised starting price. metered type, amount, currency, unit An advertised rate per Service-defined unit. quote type A later operation determines the price. For range, minimum MUST be less than or equal to maximum. A Price Preview excludes taxes, shipping, discounts, buyer-specific terms, fees, availability, and final quote results unless the Offering explicitly states otherwise outside the core price object. A live MPP or x402 challenge, quote response, or other subsequent operation is authoritative for the amount and settlement choices presented at execution time. A Price Preview MUST NOT be treated as a payment authorization or settlement requirement. If an authoritative subsequent value differs from the Price Preview, an Agent MUST use and present the authoritative value rather than silently relying on the preview. An Agent encountering an unknown Price Preview type treats only that price object as unsupported. The Offering and its unrelated fields remain usable. This permits compatible addition of future Price Preview discriminators.

Actions A Full Offering MAY contain actions, a non-empty array of operations that can follow discovery. An Offering with no advertised action omits the field. A Terse Offering MUST NOT contain actions; when permitted by the common representation rules it can advertise /actions through detail_fields. An Action describes an executable HTTP transition associated with its Offering. It does not define a commerce workflow, payment behavior, or the domain-specific shape of the operation's successful result. An Action has required authentication, id, and rel members, can contain description, and contains exactly one of http or openapi. An Offering contains at most 16 Actions, and their id values MUST be unique within that Offering. Action identifiers use the Local Resource Identifier syntax and remain stable while the Action exists on that Offering. authentication is not-required, optional, or required and has the same meanings as on an Operation Descriptor, applied to execution of that Action at the Action target. The Action target remains the authority for execution semantics; OpenAPI metadata is optional enrichment and is not required to express authentication or payment behavior. rel states the broad result sought from the operation. It is a lower-case token of at most 64 characters using letters, digits, and internal hyphens. This specification defines five values: Relation Meaning download Retrieve a downloadable representation, whether free or paid. purchase Complete a one-time acquisition. quote Obtain current terms without completing an acquisition. reserve Hold or allocate a resource. invoke Execute an online capability and obtain its result. free is a Price Preview type and is not an Action relation. download does not imply that an Offering is free. Recurring subscription behavior is not defined by ODP 1.0. An Agent encountering an unknown rel retains the Action but MUST NOT automatically select it based on an assumed meaning. A caller can explicitly select the Action by id.

Compact HTTP Target http describes an operation that does not need a complete interface description. It contains a required Resource Reference href and a required method of GET or POST. It can contain a non-empty request object and a non-empty response_content_types array of at most eight unique media types. Parameters, multiple request-body alternatives, complex responses, or declared security requirements require an OpenAPI target instead. request describes one optional request body. It contains at least one of content_type or schema. content_type identifies the body media type. schema is a JSON Schema reference with a required Resource Reference url and follows the retrieval, resolution, caching, vocabulary, and narrow-failure rules defined for Attribute Schemas. The schema describes only the Action request body. It does not describe URL, header, or cookie parameters. An Agent MUST NOT send a request body unless the caller supplies one or the operation definition supplies a complete value. response_content_types advertises media types the successful operation can return. It does not constrain authentication, payment, redirection, Problem Details, or other non-success responses. The live response Content-Type remains authoritative.

OpenAPI Target openapi identifies exactly one operation in an OpenAPI 3.1 document . It contains an optional Resource Reference url and a required case-sensitive operation_id of at most 128 Unicode code points. When url is absent, the Service Document MUST contain http.openapi.url, and that value is used. An Action-level url overrides the Service-wide value. An Action is unusable if neither reference exists. The referenced document MUST use an openapi version in the 3.1.x line and MUST contain exactly one Operation Object whose operationId equals operation_id. An Agent MUST NOT guess an operation from a path, method, summary, description, or similar identifier when that lookup fails or is ambiguous. OpenAPI retrieval is anonymous. An Agent MUST NOT attach AEP credentials, payment credentials, cookies, or authorization fields copied from the Offering request. Agents accept JSON represented as application/vnd.oai.openapi+json with a version=3.1 parameter or application/json; missing, malformed, non-JSON, or other media types are rejected. Standard HTTP caching applies. The decoded document is limited to 1,048,576 bytes, JSON depth 32, and five redirects. An invalid Action, failed request-schema retrieval, failed OpenAPI retrieval, or unresolved operation_id makes only that Action unusable. Duplicate Action IDs make every Action bearing that ID unusable. Unrelated Actions and Offering fields remain usable. An Agent-oriented SDK exposes these failures as scoped issues rather than rejecting the entire Offering. Action metadata is descriptive. A live AEP, MPP, x402, or other HTTP challenge is authoritative for access and payment. An Agent MUST NOT execute an action whose request, authorization, payment, or security consequences it cannot determine. Payment protection and Action meaning are independent. Paying to retrieve an ODP Offering grants access to that Offering representation and MUST NOT be interpreted as acquiring the Offering. An Agent invokes the separate Action target in its current authentication context and follows live AEP and payment challenges according to the composition rules in this document. A successful Action response is interpreted according to the compact metadata or OpenAPI operation, not as an ODP Offering response unless that operation explicitly returns one.

Offering Granularity A Service chooses the granularity of its Offerings. A variant that can be independently retrieved, quoted, reserved, acquired, or paid for SHOULD have its own Local Resource Identifier and Offering. Attributes can describe variants that are not independently actionable. This guidance does not define a universal variant model or require a Service to mirror its internal catalog structure.

Extensibility Model

Core Evolution Agents MUST ignore additive JSON object members they do not understand unless another rule in this document requires the containing object or capability to be rejected. Services MUST NOT use an unknown member to change the semantics of a core member. An Agent encountering an unknown enum or discriminator value MUST NOT substitute a known value or invent fallback semantics. It MUST treat the smallest capability, resource, or operation whose interpretation depends on that value as unsupported. Unrelated resources and operations remain usable. Security-sensitive behavior fails closed. An Agent MUST NOT execute an operation when an unknown field or value prevents it from determining the operation's identity, authorization, payment, request semantics, or security consequences. An Agent filters an unknown Operation Descriptor name, payment option, protocol descriptor name, MCP endpoint type, Resource Image type, or Service Branding Image type from the containing list. A list containing no recognized values after filtering is treated as absent. A recognized list item remains subject to every requirement for that item. An Agent treats an Operation Descriptor, payment protocol descriptor, or Action whose authentication value is a syntactically valid but unrecognized string as unsupported at that descriptor or Action boundary. A missing, non-string, or otherwise malformed required authentication member remains invalid. An Agent encountering an unknown Price Preview type omits the price object. An Action with an unknown rel remains available for explicit selection by id. An Action with an unknown HTTP method is unusable and is omitted from the containing Offering. An MCP endpoint with an unknown type is omitted without making the Service Document unusable. An Agent encountering an unknown Filter Definition type, operator, unit system, Sort Definition direction, or missing-value placement treats only that definition as unsupported. A Resource Identity with an unknown type is invalid. An unknown Problem Details member does not make the problem response invalid. An unrecognized problem code is interpreted using the HTTP status and standard Problem Details members. An Agent ignores an invalid-parameter entry whose in value it does not recognize.

Service-Defined Offering Data ODP defines stable envelope fields needed for discovery and link traversal. Domain-specific Offering data belongs in the Service-defined attributes object. When present, its Attribute Schema MUST identify the structure, types, and constraints of that value using JSON Schema Draft 2020-12 . An Attribute Schema can be shared across multiple Offerings. The schema's titles, descriptions, examples, and constraints help an Agent compare unfamiliar attributes without requiring the ODP core specification to standardize every domain. Filter identifiers are local to the operation or scope that advertises them. A small Service MAY embed Filter Definitions in an ODP representation. A large Service MAY link to a separate, pageable filter-definition resource. An Agent MUST interpret a filter identifier using the definition advertised for the operation and scope in which the filter is used. A Service Document SHOULD contain only Service-level discovery metadata and operation advertisement. Collection-specific or high-cardinality definitions SHOULD be linked from the narrowest applicable Collection or operation so that a Service Document remains bounded as the catalog grows.

Filters and Sorting

Capability Identifiers A Filter Definition and Sort Definition contains a Service-created capability identifier. It is a case-sensitive ASCII string of 1 through 64 characters from ALPHA, DIGIT, ., _, ~, and -. It is compared byte for byte and is not percent-decoded or Unicode-normalized. A capability identifier is not a Local Resource Identifier and does not identify an independently retrievable ODP resource. Its meaning is scoped by the Service Origin, operation, capability source, definition kind, and identifier. The same spelling can have different meanings at different Services or scopes. Capability advertisement, inheritance, and conflict rules define the effective scope in which a reference is resolved.

Filter Value Model A Filter Definition maps each Offering to a set containing zero or more scalar values of one declared type. The mapping can use core Offering metadata, Service-defined attributes, computed catalog data, an external index, or another Service implementation detail. It does not expose a storage path and need not correspond to a serialized Offering field. The core filter types and their wire values are: Type Wire value string JSON string. boolean JSON Boolean. integer JSON integer. number JSON number. decimal Base-10 JSON string without an exponent. date RFC 3339 full-date JSON string. date-time RFC 3339 date-time JSON string identifying an instant on the UTC timeline. A decimal value contains an optional minus sign, an integer part that is either zero or a nonzero digit followed by zero or more digits, and an optional fractional part containing a period followed by one or more digits. Decimal equality and ordering are numeric, not lexical, so 1.0 and 1.00 compare equal. Integer and number comparison is numeric. Boolean equality follows JSON Boolean equality. Date comparison follows calendar order. Date-time equality and ordering use the represented instant. String equality is case-sensitive Unicode scalar-value equality; ODP performs no normalization or locale folding.

Filter Definitions A Filter Definition contains id, title, description, type, and operators. title is a non-empty string of no more than 128 Unicode code points. description is a non-empty string of no more than 1024 Unicode code points. operators is a non-empty array of unique supported core operators. A numeric Filter Definition MAY contain unit; other types MUST omit it. A definition that supports value-count refinement contains refinable with the value true; otherwise it omits refinable. A refinable definition MUST advertise eq, in, or both. Every operator advertised by a Filter Definition MUST be compatible with its type: Operator Compatible types eq All core filter types. in All core filter types. lt integer, number, decimal, date, and date-time. lte integer, number, decimal, date, and date-time. gt integer, number, decimal, date, and date-time. gte integer, number, decimal, date, and date-time. exists All core filter types.

Units A unit is an inline object whose system is ucum or service. A UCUM unit contains system and code; code is a valid case-sensitive UCUM code as defined by . A Service-defined unit also contains title, a non-empty human-readable name of no more than 128 Unicode code points. Its code uses the capability-identifier syntax. Every value supplied to a Filter Expression uses the unit declared by its Filter Definition, so the request does not repeat the unit. A missing unit means that the values are categorical or dimensionless. Agents can interpret and convert compatible UCUM values. A Service-defined unit is meaningful only in that Service and capability scope; an Agent MUST NOT infer equivalence or conversion from similar codes or titles. A unit is fully defined inline and does not require URL retrieval.

Filter Expressions filters is a non-empty array of no more than 32 Filter Expressions. Each expression contains id, operator, and value. id MUST resolve to an effective Filter Definition for the operation and scope. The operator MUST be advertised by that definition, and the value MUST conform to the definition's type and the following shape: Operator Request value eq, lt, lte, gt, gte One scalar of the Filter Definition's type. in An array of 1 through 100 unique scalars of the Filter Definition's type. exists A JSON Boolean. For eq, an Offering matches when at least one mapped value equals the request value. For in, it matches when its mapped set and the request set intersect. For a comparison operator, it matches when at least one mapped value satisfies the comparison. For exists: true, it matches when the mapped set is non-empty; for exists: false, it matches when that set is empty. Every Filter Expression in one request combines with logical AND. The same identifier can appear more than once, which permits bounded ranges such as gte and lte. in expresses logical OR among accepted values for one Filter Definition. ODP version 1.0 defines no general Boolean expression tree, negative operator, substring operator, or regular-expression operator. An unknown identifier, unadvertised or incompatible operator, invalid value, excessive expression count, or excessive in cardinality produces an INVALID_REQUEST problem.

Refinements refinements in an Offering-search request is a non-empty array of at most 16 unique capability identifiers. Every identifier MUST resolve to an effective Filter Definition whose refinable member is true. An unavailable, invalid, quarantined, duplicate, or non-refinable identifier produces an INVALID_REQUEST problem. A Service that advertises no refinable Filter Definitions does not implement refinement computation. An initial Offering-search response MAY contain refinements only when the request contains it. The response member is a non-empty array of at most 16 Refinement Groups. Each group contains filter_id and values; filter_id MUST occur in the request and MUST be unique among the returned groups. A Service MAY omit a requested group when it cannot produce useful values. An omitted group does not invalidate other groups or the Offering results. values contains 1 through 32 Refinement Buckets whose values are unique under the referenced Filter Definition's equality semantics. Each bucket contains value and count. value MUST be a scalar valid for the referenced Filter Definition's type. count is a non-negative JSON integer no greater than 9,007,199,254,740,991. An exact count omits count_relation. A count known only to be a lower bound contains count_relation with the value lower_bound. A Service MUST NOT report an estimate as exact. For one bucket, the Service evaluates the original Collection constraint, query, access context, and every Filter Expression whose identifier differs from the group's filter_id. It then applies the bucket value to the referenced Filter Definition using its equality semantics. count is the number of distinct matching Offerings. Removing same-filter expressions makes alternative values useful for navigation while retaining every independent constraint. Sorting and page limits do not affect the count. Refinement values are contextual suggestions, not a complete enumeration of a Filter Definition's domain and not another capability source. An Agent resolves filter_id through the effective capability catalog and interprets every bucket using that definition's type and unit. ODP does not define total-result counts; a bucket count applies only to that candidate value. An Agent-oriented SDK SHOULD return normalized groups with their resolved Filter Definitions and scoped issues rather than requiring its caller to join raw identifiers.

Sort Definitions A Sort Definition advertises one complete ordering recipe that the Service can execute. It contains id, title, description, and keys. title and description use the Filter Definition string limits. keys is an array of 1 through 3 Sort Keys. Each Sort Key contains filter_id, direction, and missing. Every filter_id MUST be distinct and resolve to an effective Filter Definition in the same operation and scope. direction is ascending or descending; missing is first or last. For a Sort Key whose Filter Definition maps an Offering to multiple values, ascending selects the minimum value and descending selects the maximum value before ordering Offerings. Numeric, decimal, date, and date-time values use the comparison semantics defined for filters. The Service defines type-appropriate string collation and MUST describe non-obvious collation in the Sort Definition. The advertised key sequence, directions, and missing-value placement are fixed. The Agent selects a recipe through the search request's sort member and MUST NOT add, remove, reverse, or reorder its keys. The Service MUST append Offering id as the final ascending tie-breaker after all advertised keys. The resulting order is subject to the common stable-pagination contract. An absent sort selects the Service's preferred ordering and does not require a Sort Definition. An unknown or unavailable Sort Definition identifier produces an INVALID_REQUEST problem.

Search Capability Advertisement search_capabilities is an object that contains at least one of filters or sorts. A Service Document advertises Service-wide capabilities. A Full Collection Representation advertises capabilities specific to searches whose request explicitly names that Collection. The field MUST NOT appear unless the Service advertises search-offerings. filters and sorts are independent capability sources. Each source contains exactly one of inline or linked. inline is a non-empty array containing no more than 32 Filter Definitions or 16 Sort Definitions, according to the source. linked is an object containing href, a same-origin Resource Reference to the first page of the applicable definition sequence. A source with no definitions is omitted rather than represented by an empty array. A linked source is retrieved with GET and uses application/odp+json. The response is a standard page envelope whose items contain only the applicable definition kind and whose next links obey the common continuation contract. A page contains no more than 100 definitions, and a complete linked source contains no more than 16 pages. The linked operation can enforce access policy through live HTTP challenges. It follows the common Accept-Language, Content-Language, Vary, validator, redirect, response-limit, and caching rules. The advertisement does not contain a redundant pagination flag; only next indicates another page. Each inline or complete linked source is atomic. An Agent MUST retrieve and validate every page, enforce source uniqueness and bounds, and only then expose definitions from that source. It MUST NOT expose an earlier page while later pages remain unresolved. A failed or invalid source is omitted from the normalized capability catalog and reported as a scoped issue. Once a linked source cannot fit within the applicable effective-catalog bound, the Agent MUST stop retrieving that source and discard it. If page 16 contains next, the Agent MUST NOT retrieve page 17 and MUST discard the source. Failure of a Collection-specific source does not invalidate a valid Service-wide source, and capability failure does not prevent text-only Offering search.

Effective Search Capabilities An Offering search without collection_id uses only Service-wide capabilities. A search with collection_id uses the union of Service-wide capabilities and capabilities advertised by that exact Collection. Ancestors, descendants, and other Collections do not contribute definitions. include_descendants changes the Offering membership scope but does not change capability inheritance. The effective catalog contains at most 1,024 Filter Definitions and 128 Sort Definitions after merging its sources. The Service-wide source is applied before the selected-Collection source. Exceeding either limit makes the source that causes the overflow invalid; an Agent preserves earlier valid sources and reports a scoped issue. SDKs SHOULD retain and index the normalized catalog programmatically rather than placing every definition into an Agent's language model context. A conforming Service MUST NOT publish the same Filter Definition identifier or Sort Definition identifier in two effective sources, even when their serialized definitions are equal. An Agent quarantines each cross-source duplicate identifier rather than selecting an override. It also quarantines every Sort Definition that references a missing, invalid, or quarantined Filter Definition. Unrelated definitions remain usable. A request using a quarantined or otherwise unavailable identifier produces an INVALID_REQUEST problem. An Agent-oriented SDK SHOULD expose one normalized effective capability catalog containing valid Filter Definitions and resolved Sort Definitions, plus scoped issues. Callers need not process raw capability pages, merge scopes, detect conflicts, or resolve Sort Definition references.

Composition Boundaries ODP describes resources and references that lead to subsequent operations. It does not duplicate the semantics of those operations. A Service MAY make ODP resources public, require AEP enrollment before some or all ODP operations, require MPP or x402 payment, or combine these protocols in a Service-selected order. Capability metadata is descriptive. Live HTTP authentication and payment challenges are authoritative for the credentials, payment requirements, and retry mechanics of the request being made. An advertised authentication requirement does not replace those challenges. The following signals belong to their defining protocols and are not redefined by ODP: Protocol Live signal AEP 401 Unauthorized with an AEP challenge in WWW-Authenticate. MPP 402 Payment Required with a Payment challenge in WWW-Authenticate. x402 402 Payment Required with payment requirements in PAYMENT-REQUIRED. A Service that requires both AEP and payment for an ODP operation MUST authenticate the Agent before processing payment. Its response to a request without acceptable AEP credentials has status 401 and carries the AEP challenge, even if the request also lacks payment. After AEP authentication succeeds, the Service can return the applicable live payment challenge. An Agent begins with the requested ODP operation in its current authentication context. A valid AEP challenge causes it to complete the AEP flow and retry the same operation with an AEP credential. When payment can follow, the Agent SHOULD use the dedicated AEP-Authorization field defined by AEP so that Authorization remains available for an MPP credential. The Agent fulfills payment only after the authenticated retry returns a live payment challenge. It then retries with the AEP credential and either the MPP Authorization: Payment credential or the x402 PAYMENT-SIGNATURE field, as defined by the selected payment protocol. This sequence does not require AEP where the Service does not require enrollment. A public operation can succeed immediately, and a payment-only operation can return 402 Payment Required directly. Each retry remains subject to the credential handling, request binding, redirect, replay, and error rules of the protocol that caused it. A successful response means that the request did not require another challenge at that point, regardless of the Service-wide advertisement. A live challenge for an unadvertised protocol is still authoritative. An advertised protocol without a corresponding live challenge MUST NOT cause an Agent to enroll, authenticate, or pay speculatively. An Agent MUST NOT infer that support for ODP implies support for AEP, MPP, x402, or any other protocol. An Agent MUST NOT infer that support for one composition order implies support for another.

Errors and Limits

Problem Details An error generated by ODP request processing with a response body MUST use Problem Details as defined by and the application/problem+json media type. A response governed by a live authentication or payment challenge protocol retains that protocol's body rules. The Problem Details object MUST contain type, title, status, and code. detail and instance are optional. status MUST equal the HTTP response status. title contains no more than 128 Unicode code points, and detail contains no more than 2048 Unicode code points. type is an absolute HTTPS URL under https://offeringprotocol.org/problems/ identifying the problem class. code is the stable machine-readable identifier used by Agent implementations. A code contains 1 through 64 uppercase ASCII letters, digits, or underscores and begins with a letter. type MUST equal https://offeringprotocol.org/problems/<code>, where <code> is the value of code converted to lowercase ASCII and each underscore is replaced by a hyphen. An Agent MUST ignore unknown additive Problem Details members. The initial core problem codes are: Code Status Meaning INVALID_REQUEST 400 Request syntax or values are invalid. NOT_AUTHENTICATED 401 Authentication is required or invalid. NOT_AUTHORIZED 403 The principal cannot perform the operation. NOT_FOUND 404 The requested ODP resource does not exist. NOT_ACCEPTABLE 406 No acceptable response representation exists. CONTINUATION_EXPIRED 410 The continuation link has expired. REQUEST_TOO_LARGE 413 The request exceeds its resource limit. UNSUPPORTED_MEDIA_TYPE 415 The request media type is unsupported. RATE_LIMITED 429 Request rate or quota has been exceeded. SERVICE_UNAVAILABLE 503 The Service is temporarily unable to respond. Later compatible protocol revisions can define additional codes. An Agent encountering an unknown code MUST use the HTTP status and standard Problem Details members as its fallback semantics. It MUST NOT reinterpret an unknown code as a known one. Live HTTP authentication and payment challenges remain authoritative. A Problem Details body does not replace WWW-Authenticate, MPP, x402, AEP, or another challenge header, and an Agent MUST preserve those headers for the applicable protocol handler.

Invalid Parameters An INVALID_REQUEST problem MAY contain invalid_params, a non-empty array of parameter failures. Each entry contains in, name, and reason. in is one of query, body, header, or path. For a body member, name is a JSON Pointer as defined by . For another location, name is a non-empty parameter or header name. name contains no more than 256 Unicode code points, and reason is a non-empty concise explanation of no more than 1024 Unicode code points. The array contains no more than 32 entries. An Agent MUST NOT parse reason to determine recovery behavior.

Agent Error Results An Agent-oriented SDK SHOULD map an operation failure to a typed error containing at least code, message, and retryable. It can also expose retry timing and structured invalid parameters. A failed requested operation is an error, not a partial-result issue. A scoped enrichment failure that does not invalidate the requested ODP resource, such as an unavailable Attribute Schema, remains an issue under the applicable SDK result contract.

Resource Limits Limits apply after HTTP content codings are decoded and before a representation is exposed to an Agent caller. JSON depth is measured from the top-level value. A Service MUST produce documents within the applicable limits, and an Agent MUST stop reading a body when it exceeds its applicable byte limit. Resource Limit ODP request body 65,536 bytes Individual Collection or Offering response 524,288 bytes List, search, or Filter Definition page 524,288 bytes Problem Details response 16,384 bytes JSON nesting depth except Service Document 16 Service Document 65,536 bytes Service Document nesting depth 8 Items per page 100 Pages per linked capability source 16 One Attribute Schema document 262,144 bytes Complete Attribute Schema reference graph 1,048,576 bytes One OpenAPI Action document 1,048,576 bytes Distinct documents in one schema graph 16 Attribute Schema reference depth 8 Redirects per retrieved resource 5 The more specific Service Document, field, relationship, and pagination limits elsewhere in this document continue to apply. A Service MAY return fewer page items than requested to remain within the page limit. Domain-specific attribute arrays are bounded by their Attribute Schema and the overall byte and depth limits rather than by a universal element count. Every redirect target for an ODP resource, JSON Schema resource, or OpenAPI Action document MUST retain the scheme, host, and effective port of the preceding request. An Agent MUST reject redirect loops, transport security downgrades, and a sixth redirect. A cross-origin Resource Reference can initiate a request to its explicit origin; that resource cannot use redirects to transfer the request to another origin.

Limit Failures A receiver MUST NOT truncate and expose partial JSON, a partial schema, a partial string, or a partial array. It rejects the affected document before exposing any of that document's contents. Valid items yielded from earlier pages remain valid, but automatic pagination stops at the failing page. An Agent-oriented SDK reports a local RESPONSE_LIMIT_EXCEEDED error for the failed operation. An Attribute Schema limit failure makes the corresponding attributes uninterpretable. The SDK omits those attributes from its normalized result and reports a scoped issue; unrelated Offering fields remain usable. A Service receiving an oversized ODP request returns 413 Content Too Large with REQUEST_TOO_LARGE Problem Details.

Rate Limits and Retries A 429 Too Many Requests response MUST include Retry-After. A 503 Service Unavailable response SHOULD include it. An Agent-oriented SDK SHOULD support bounded automatic retry for these statuses. The default policy performs at most three retries and spends at most 30 seconds waiting across the operation. It honors Retry-After when doing so does not exceed that elapsed-time limit; otherwise it returns the typed error without waiting. When Retry-After is absent on 503, the SDK uses bounded exponential backoff with jitter. ODP list, search, and retrieval operations are read-only at the application layer and can be retried under this policy. An SDK MUST NOT automatically restart an expired continuation or retry an authentication, authorization, validation, or other non-transient failure.

Compatibility of Errors The core evolution rules apply to successful and unsuccessful documents. Unknown additive members are ignored. Unknown Problem Details codes fall back to HTTP status semantics. Unknown discriminators disable only the smallest dependent capability, and security-sensitive ambiguity fails closed. An unsupported odp_version rejects an ODP document as defined in Protocol Versioning.

Conformance An implementation claims conformance separately for the Agent and Service roles. ODP defines one required baseline for each role. It does not define named conformance levels, profiles, or a minimum capability.

Service Baseline A conformant ODP Service: publishes a valid, publicly retrievable Service Document at /.well-known/odp; advertises and implements list-offerings and get-offering using its advertised endpoint base; implements the shared versioning, media type, representation, pagination, localization, caching, error, limit, redirect, and security requirements applicable to those operations; and satisfies every Service requirement for each additional operation, protocol, search feature, or per-resource feature it advertises or returns. The Offering sequence can be empty. A Full Offering still requires only odp_version, id, and name; Actions, prices, attributes, schemas, Collection membership, and other optional fields do not become required by baseline conformance.

Agent Baseline A conformant ODP Agent: retrieves and validates the Service Document; invokes list-offerings, follows its continuation sequence, and processes Terse and Full Offering representations; invokes get-offering and processes a Full Offering; and implements the shared versioning, media type, representation, pagination, localization, caching, error, limit, redirect, compatibility, and security requirements applicable to those operations. An Agent can omit Collections, search, filters, sorting, refinements, Attribute Schema resolution, Actions, and external protocol composition. It MUST ignore or narrowly isolate unsupported optional data according to this document and MUST NOT claim support for behavior it does not implement.

Runtime Advertisement and Evidence ODP defines no generic capabilities member and no secondary runtime conformance manifest. Runtime support is advertised through the singular odp_version, operations, protocols, search_capabilities, mcp, and applicable per-resource members such as schema and actions. An implementation MUST NOT add a parallel claim that can contradict those authoritative fields. A conformance harness can generate release evidence identifying the implementation name and version, role, singular ODP version tested, vector revision, suites executed, and passed, failed, and skipped results. Such a report describes test evidence for one software release. It is not an ODP wire document, is not retrieved during discovery, and does not override runtime advertisement or normative requirements. Directory behavior is outside ODP conformance. Examples, guides, schemas, and test vectors support implementation and testing; they do not override normative Internet-Draft prose.

IANA Considerations

Media Type Registration This document requests registration of the following media type in the Media Types registry according to : Field Value Type name application Subtype name odp+json Required parameters None Optional parameters None Encoding considerations Binary; the representation is a JSON document encoded in UTF-8. Security considerations See the Security Considerations section of this document. Interoperability considerations The odp_version member identifies the exact protocol version. Published specification This document. Applications that use this media type Agents and Services implementing ODP. Fragment identifier considerations None; ODP Resource References prohibit fragments. Additional information None. Person and email address for further information IETF, iesg@ietf.org. Intended usage COMMON Restrictions on usage None. Author IETF Change controller IETF

Well-Known URI Registration This document requests the following registration in the Well-Known URIs registry defined by :

URI suffix: odp
Change controller: IETF
Specification document: This document
Related information: None

Security Considerations

Untrusted Content and Agent Control Every ODP representation, string, schema, OpenAPI document, URL, cursor, and Action is untrusted network input. An Agent MUST validate a representation before using its Service-defined data or following its references. Names, descriptions, keywords, schema annotations, examples, and other human-readable content are data; they MUST NOT supersede caller intent, implementation policy, protocol requirements, or higher-priority Agent instructions. An implementation MUST safely encode untrusted strings for its output context. It MUST NOT interpret terminal control sequences, markup, code fragments, schema keywords, OpenAPI extensions, or media type parameters as executable instructions. JSON Schema formats and regular expressions can consume unbounded computation in some engines. Agents MUST apply documented time, memory, recursion, and evaluation limits and MUST NOT load executable code to process a schema or OpenAPI extension.

Network Request and SSRF Protection Resource References can identify a different origin only through an explicit absolute HTTPS URL. Cross-origin support does not grant unrestricted network access. Before each connection, an Agent MUST resolve the target host and reject every destination address that is loopback, private-use, link-local, multicast, unspecified, reserved, documentation-only, or otherwise non-public according to the IANA special-purpose address registries described by . If a resolution returns both public and non-public addresses, the Agent MUST reject the target rather than select one result. The Agent MUST verify that the connected peer address is one of the public addresses it validated for that request. It MUST repeat resolution and validation for every new connection, retry, and redirect to prevent DNS rebinding and time-of-check/time-of-use substitution. The same policy applies when a proxy or custom resolver performs the connection; an implementation MUST NOT use either to bypass destination policy. The local-development HTTP exception applies only when local development is explicitly enabled and the URL host is syntactically localhost, 127.0.0.1, or [::1]. A DNS name that resolves to a loopback or other non-public address does not qualify. Production defaults MUST keep local-network access disabled. Implementations MAY impose stricter port, domain, origin, network, or enterprise egress allowlists. Every redirect remains limited to the preceding request's origin. A cross-origin Resource Reference can initiate an independently validated request to its explicit origin, but neither a redirect nor a DNS change can transfer that request to another origin or a non-public destination.

Credential and Payment Isolation An Agent applies origin and credential policy independently to every request. Retrieval of a JSON Schema, OpenAPI document, or other supporting metadata is anonymous. Such a request MUST NOT contain cookies, AEP credentials, payment credentials, caller authorization fields, or secrets copied from the referring request. An Agent MUST NOT copy a credential, enrollment artifact, payment proof, cookie, or authorization field to another origin solely because an ODP representation links there. A cross-origin Action begins without credentials belonging to the Offering Service. Credentials for the Action target can be obtained or sent only under the target origin's applicable protocol and live challenge rules. Redirect processing strips all sensitive fields before any separately authorized request begins. An advertised protocol, Price Preview, Action relation, schema annotation, or OpenAPI security declaration is not authorization to enroll, authenticate, or pay. A live challenge remains authoritative for protocol mechanics but does not override caller approval, spend limits, accepted assets, destination policy, or other payment policy. An Agent MUST present a changed authoritative amount or settlement choice to its policy layer rather than silently relying on discovery metadata.

Action Safety Discovering, parsing, validating, or resolving an Action MUST NOT invoke its target. An Agent invokes an Action only after a caller explicitly selects its id and supplies or approves the required inputs. Unknown relations are never selected automatically. Implementations MUST NOT prefetch an Action target as an optimization; retrieving a separately identified request schema or OpenAPI document does not invoke the Action. Services MUST implement a compact GET Action with safe HTTP semantics as defined by . An Agent MUST NOT automatically retry a state-changing Action after an ambiguous outcome unless the operation defines an applicable idempotency mechanism and the retry preserves it. AEP, MPP, and x402 challenge-response retries remain governed by their defining protocols and the exact request binding.

MCP Endpoint Safety An advertised MCP Endpoint is an untrusted network destination. A client that elects to connect MUST apply the Resource Reference, destination-address, redirect, and credential-isolation requirements to the resolved endpoint. A cross-origin MCP Endpoint starts without credentials belonging to the ODP Service Origin. The client follows MCP's current transport and authorization requirements and MUST NOT infer authentication state, supported capabilities, or safe tool behavior from the ODP descriptor.

Resource Exhaustion and Abuse Implementations MUST enforce the decoded-size, nesting-depth, schema-graph, page, redirect, retry, and elapsed-time limits in this document before exposing a result. Compression does not increase a limit. A receiver fails closed when a complete document cannot be obtained within its bounds and never treats a truncated document as valid. Agents MUST bound concurrent Service, page, schema, OpenAPI, and Action-related work. Cursors and Service-defined identifiers are untrusted and provide no authorization. Services SHOULD apply request-rate, query-complexity, and concurrency controls without exposing private catalog existence through distinguishable errors.

Cache Poisoning and Staleness An Agent MUST honor Cache-Control, Vary, validators, authorization context, and the cache rules in this document. Cache entries are scoped by the effective request URL, method, representation and localization inputs, and authentication context required by HTTP. A response obtained in an authenticated or private context MUST NOT be reused as a public response. Validators from one URL or origin MUST NOT validate a representation from another. Cached discovery metadata, schemas, and OpenAPI documents can become stale or maliciously inconsistent. They never authorize access, payment, or Action execution. Live responses and current resource state remain authoritative, and a contradiction triggers narrow failure or revalidation rather than merging fields from conflicting representations.

Privacy Considerations Discovery requests can reveal user interests, intended purchases, location constraints, or business plans. Agents SHOULD minimize disclosed query data and avoid sending user-specific context that is not needed for the operation. Cross-origin schema and OpenAPI retrieval discloses the Agent's network address, timing, and interest in the referring Service or Offering to another operator. Agents SHOULD retrieve only supporting resources needed for the caller's operation, avoid eager resolution of every advertised Action, and apply privacy-preserving network policy where appropriate. Sensitive values MUST NOT be placed in Resource Reference query strings, logs, telemetry, cache keys visible to unrelated tenants, or Problem Details intended for another party. Services SHOULD minimize data returned in Terse Representations and apply access controls before returning sensitive Offering attributes. Directories SHOULD limit indexed data to public Service metadata and document their retention and refresh policies. auth_expands reveals only that authentication can expand the current result. A Service MUST NOT use detail_fields, result counts, identifiers, refinement counts, errors, timing differences, or other metadata to disclose the nature or quantity of protected content to a principal that is not permitted to learn it.

Acknowledgements The protocol design is informed by practical requirements from agent-native commerce, service discovery, and large catalog systems.