Specifications

The specifications that define API contracts, message formats and schemas, with the current version of each.

All specifications

Agent2Agent Protocol (A2A)A reference for the Agent2Agent protocol, covering Agent Cards and discovery, tasks, messages and artifacts, the JSON-RPC, gRPC and HTTP+JSON bindings, streaming and push notifications, and how A2A differs from MCP.1.0

api-catalog (RFC 9727)A reference for RFC 9727, which defines the /.well-known/api-catalog URI and the api-catalog link relation so clients can discover a publisher's APIs, their descriptions and their documentation from a known location.RFC 9727
Arazzo SpecificationA comprehensive, multi-section breakdown of the Arazzo specification, explaining workflows orchestration, input-output expressions, and state assertions.1.1.0
AsyncAPI SpecificationA deep-dive explanation of the AsyncAPI Specification, detailing message-driven architectures, channels, protocols, and event bindings.3.1.0
Building Protocols with HTTP (RFC 9205, BCP 56)A reference for RFC 9205, the IETF's Best Current Practice for designing applications on top of HTTP: generic semantics, links over fixed paths, registered methods and status codes, header fields, caching, and how to version and evolve an HTTP API.RFC 9205 (BCP 56)
CloudEventsAn overview of the CloudEvents specification, the CNCF standard for describing event data in a common, vendor-neutral format.1.0.2
Connect and gRPC-WebA reference for the two protocols that carry Protocol Buffers RPCs to browsers and over HTTP/1.1: the Connect protocol, with plain JSON unary calls, GET for side-effect-free methods and JSON errors, and gRPC-Web, with trailers in the body and a translating proxy.Connect protocol v1; gRPC-Web (PROTOCOL-WEB)
Date and Time on the Internet (RFC 3339)A reference for RFC 3339, the profile of ISO 8601 that JSON APIs use for timestamps: the date-time grammar, offsets, Z and -00:00, fractional and leap seconds, the RFC 9557 time zone suffix, and how it differs from ISO 8601 and HTTP-date.RFC 3339 (updated by RFC 9557)
Deprecation and Sunset Headers (RFC 9745, RFC 8594)A reference for the two HTTP response fields that announce the end of a resource: Deprecation (RFC 9745) for when it stopped being recommended, Sunset (RFC 8594) for when it will stop responding, and the deprecation and sunset link relations.RFC 9745 / RFC 8594
Digest Fields (RFC 9530)A reference for RFC 9530, which defines Content-Digest and Repr-Digest for HTTP integrity, the Want-Content-Digest and Want-Repr-Digest preference fields, and the hash algorithm registry, and obsoletes RFC 3230's Digest header.RFC 9530
DPoP: Demonstrating Proof of Possession (RFC 9449)A reference for RFC 9449, which binds OAuth access and refresh tokens to a client-held key: the DPoP proof JWT and its claims, the DPoP authorization scheme, server-supplied nonces, the cnf jkt binding, and how resource servers validate a proof.RFC 9449
GraphQLA query and schema definition language specification for APIs, providing a client-specified runtime to request exact data shapes.September 2025
GraphQL over HTTPA reference for the GraphQL Foundation's GraphQL-over-HTTP specification: request parameters, GET and POST rules, the application/graphql-response+json media type, Accept negotiation for legacy clients, and the status code rules, including 294 for partial success.Stage 2 (Draft), working draft
gRPCA high-performance, open-source RPC framework that carries Protocol Buffers messages over HTTP/2, with generated clients and servers, four streaming patterns and its own status codes.gRPC over HTTP/2 (PROTOCOL-HTTP2)
HAL (Hypertext Application Language)A reference for the Hypertext Application Language, a simple hypermedia format for JSON and XML APIs, covering _links, curies, _embedded resources, and a comparison with JSON:API.draft-kelly-json-hal-11
HTTP Caching (RFC 9111)A reference guide to HTTP caching as defined in RFC 9111, covering freshness, validation, Cache-Control directives, the Vary header, shared versus private caches, and heuristic freshness.RFC 9111
HTTP Message Signatures (RFC 9421)A reference for RFC 9421, the IETF standard for signing HTTP requests and responses: covered components, derived components, the signature base, signature parameters, the algorithm registry, and requesting signatures with Accept-Signature.RFC 9421
HTTP Semantics (RFC 9110)The foundational reference for HTTP, RFC 9110 defines the version-independent semantics of the protocol: methods, status codes, header fields, representations, content negotiation, conditional and range requests, and the authentication framework.RFC 9110
HTTP/1.1 (RFC 9112)A reference guide to HTTP/1.1 as defined in RFC 9112, covering the text message format, request-target forms, message body length, chunked transfer coding, persistent connections and pipelining, and the framing rules that defend against request smuggling.RFC 9112
HTTP/2 (RFC 9113)A reference guide to HTTP/2 as defined in RFC 9113, covering binary framing, multiplexed streams over a single connection, HPACK header compression, stream prioritization, and the transport-layer head-of-line blocking that HTTP/3 later addressed.RFC 9113
HTTP/3 (RFC 9114)A reference guide to HTTP/3 as defined in RFC 9114, the version of HTTP that runs over QUIC to eliminate transport-layer head-of-line blocking, with QPACK header compression, 0-RTT, connection migration, and Alt-Svc discovery.RFC 9114
Idempotency-Key Header Field (Internet-Draft)A reference for draft-ietf-httpapi-idempotency-key-header, the IETF HTTPAPI draft that standardizes the Idempotency-Key request header for making POST and PATCH safely retryable: key syntax, fingerprints, expiry and the 400, 409 and 422 error cases. Expired, not an RFC.draft-ietf-httpapi-idempotency-key-header-07 (expired)
JOSE: JWS, JWE, JWK and JWA (RFC 7515-7518)A reference for the JSON Object Signing and Encryption suite: JWS signatures, JWE encryption and its five-part compact form, JWK keys and key sets, the JWA algorithm registry, the compact and JSON serializations, and the alg pitfalls behind most JWT vulnerabilities.RFC 7515, 7516, 7517, 7518
JSON Lines and NDJSONA reference for newline-delimited JSON: the JSON Lines and NDJSON conventions, their rules for encoding and line endings, the unregistered media type situation, and RFC 7464 JSON Text Sequences as the IETF alternative.JSON Lines / NDJSON 1.0.0
JSON Merge Patch (RFC 7396)A reference for JSON Merge Patch, the document-shaped format for partial updates with PATCH, covering the merge algorithm, null-as-delete semantics, array replacement, and when the format is the wrong choice.RFC 7396
JSON Patch (RFC 6902)A reference for JSON Patch, the operation-based format for partial updates with PATCH, covering the six operations, JSON Pointer paths, the test operation, atomicity, and error handling.RFC 6902
JSON Pointer (RFC 6901)A reference for JSON Pointer, the string syntax for identifying a single value in a JSON document, covering ~0 and ~1 escaping, the URI fragment form, the array '-' token, and its use in JSON Patch, JSON Schema and problem details.RFC 6901
JSON Schema in Web APIsAn authoritative guide to JSON Schema, detailing validation vocabulary, conditional schemas, logical operators, and $ref definition resolving.Draft 2020-12
JSON Web Token (JWT)A technical reference for JSON Web Tokens, covering the header/payload/signature structure, registered claims, JWS versus JWE, signing algorithms, and common validation pitfalls.RFC 7519
JSON-LD & HydraA reference for JSON-LD linked data and the Hydra vocabulary, covering @context, @id, @type, hypermedia-driven operations and collections, and a comparison with HAL and JSON:API.JSON-LD 1.1
JSON-RPC 2.0A minimal, transport-agnostic remote procedure call protocol in JSON: requests, responses, notifications, batches and the reserved error codes, and the base protocol under MCP.2.0
JSON:API SpecificationA detailed breakdown of the JSON:API specification, explaining compounds documents, relations, sparse fieldsets, sorting, and pagination models.1.1
Linkset (RFC 9264)A reference for RFC 9264, which defines application/linkset and application/linkset+json for publishing sets of web links as a standalone document, plus the linkset link relation for discovering them.RFC 9264
Model Context Protocol (MCP)A reference for the Model Context Protocol, covering its JSON-RPC 2.0 base, host, client and server roles, tools, resources and prompts, the stdio and Streamable HTTP transports, and OAuth-based authorization.2026-07-28
OAuth 2.0 and OAuth 2.1A reference for the OAuth 2.0 authorization framework (RFC 6749, RFC 6750) and the OAuth 2.1 draft, covering roles, grant types, PKCE, the RFC 9700 security BCP, token revocation and introspection, and server metadata.RFC 6749 (OAuth 2.1 in draft)
OAuth 2.0 Security Best Current Practice (RFC 9700)A reference for RFC 9700 (BCP 240), the IETF's current security baseline for OAuth 2.0: exact redirect URI matching, mandatory PKCE, the end of the implicit and password grants, sender-constrained tokens, refresh token rotation and mix-up defenses.RFC 9700 (BCP 240)
OData (Open Data Protocol)An overview of the OData specification, covering standardized query conventions, resource modeling, and where it fits alongside ad-hoc REST APIs.4.01
OpenAPI Overlay SpecificationThe OpenAPI Initiative format for describing repeatable changes to an OpenAPI document: JSONPath targets, update, remove and copy actions, applied in order.1.2.0
OpenAPI Specification (OAS)A comprehensive, multi-section guide to the OpenAPI Specification (OAS), detailing root structures, paths, component registries, and version diffs.3.2.1
OpenID Connect (OIDC)A reference for OpenID Connect, the identity layer on top of OAuth 2.0, covering the ID Token, the authorization code flow with PKCE, the UserInfo endpoint, discovery, and standard scopes.1.0
OpenTelemetryThe CNCF standard for producing and exporting traces, metrics and logs: the API and SDK model, the OTLP wire protocol, HTTP semantic conventions and the Collector.1.61.0
Problem Details for HTTP APIs (RFC 9457)A reference for the application/problem+json format, covering the standard members, extension members, and validation error patterns used to communicate HTTP API errors.RFC 9457
Protocol BuffersGoogle's language-neutral schema language and binary serialization format: proto3 and Editions, the wire format, field numbers, the rules for evolving a schema safely, and the JSON mapping.Edition 2024
RateLimit Header Fields (Internet-Draft)A reference for draft-ietf-httpapi-ratelimit-headers, the IETF HTTPAPI draft that defines the RateLimit and RateLimit-Policy fields, quota units, partition keys and rate limit problem types. An active Internet-Draft, not yet an RFC.draft-ietf-httpapi-ratelimit-headers-11
Resumable Uploads for HTTP (Internet-Draft)A reference for draft-ietf-httpbis-resumable-upload, the IETF HTTP working group draft for resuming interrupted uploads: upload resources, the Upload-Offset, Upload-Complete, Upload-Length and Upload-Limit fields, the provisional 104 status code, and its tus origins. An active Internet-Draft, not yet an RFC.draft-ietf-httpbis-resumable-upload-13
SCIM (System for Cross-domain Identity Management)A reference for SCIM 2.0, the standard protocol for automating user and group provisioning across identity providers and applications, covering the core schema, resource endpoints, PATCH operations, and filtering.2.0
Server-Sent Events (SSE)A practical guide to Server-Sent Events, the HTML standard for one-way server-to-client streaming over a single long-lived HTTP connection using the text/event-stream media type.WHATWG Living Standard
SmithyA reference for Smithy, the protocol-agnostic interface definition language from AWS: IDL 2.0 shapes, services, resources and operations, traits, the restJson1 and rpcv2Cbor protocols, code generation, and how it relates to OpenAPI.Smithy 2.0 (IDL version 2)
SOAP and WSDLA reference for integrators meeting legacy SOAP services: SOAP 1.1 and 1.2 envelopes, the SOAPAction header and the action parameter, faults and their HTTP status codes, WSDL 1.1 and 2.0, document/literal style, and WS-Security.SOAP 1.2 (Second Edition, 2007); WSDL 1.1 / 2.0
Standard WebhooksAn open specification for sending webhooks consistently: the webhook-id, webhook-timestamp and webhook-signature headers, HMAC-SHA256 and Ed25519 signing, and delivery rules.1.0.0
Structured Field Values for HTTP (RFC 9651)A reference for RFC 9651, the common syntax for new HTTP header and trailer fields: Lists, Dictionaries and Items, parameters, the bare item types including Date and Display String, strict parsing, and which fields use it.RFC 9651
The HTTP QUERY Method (RFC 10008)A reference for RFC 10008, which defines QUERY, a safe, idempotent and cacheable HTTP method that carries the query in the request body: Content-Type rules, the Accept-Query field, Location and Content-Location, redirects and cache keys.RFC 10008
URI Template (RFC 6570)A reference for RFC 6570 URI Templates: the four levels, expression operators, the prefix and explode modifiers, how HAL and hypermedia APIs use templated links, and how OpenAPI path templating differs from RFC 6570.RFC 6570
W3C Trace ContextThe W3C Recommendation that standardizes the traceparent and tracestate headers, so a distributed trace survives every hop between services, vendors and languages.Level 1 (W3C Recommendation)
Web Linking (RFC 8288)A reference for RFC 8288, which defines the abstract model for typed links, the Link header field, the IANA Link Relations registry and extension relation types, with the relations APIs use for pagination and discovery.RFC 8288
WebSocket ProtocolA reference guide to the WebSocket Protocol defined in RFC 6455, covering the HTTP Upgrade handshake, full-duplex framing, subprotocols, and how it compares to SSE and HTTP polling.RFC 6455