OpenAPI Specification 3.1
OpenAPI is the de-facto standard for API documentation, code generation, mock servers, and contract testing. Most APIs you build should have an OpenAPI spec.
What It Defines
The standard format for describing REST/HTTP APIs: paths, operations, request/response schemas, security schemes, servers, and components. OpenAPI 3.1 fully adopts JSON Schema 2020-12 for schemas.
Canonical (Normative)
Convenient (Practical)
The canonical publication point for finalized RFCs. If a protocol is standardized as an RFC, the RFC Editor text is the normative final reference. Published by the IETF, IRTF, IAB, and independent stream.
Related Specs
JSON Schema is the standard way to document and validate API request/response shapes. OpenAPI 3.1 fully adopts it. Know it if you design APIs.
If you have event-driven systems (Kafka, RabbitMQ, WebSocket APIs, IoT), AsyncAPI is the description format. Analogous to OpenAPI for async what OpenAPI is for REST.
This is the core contract of every web API, browser request, and server response. You can't design or debug HTTP without knowing this.