The industry standard for describing HTTP APIs.
The OpenAPI Specification (OAS) is the most widely adopted standard for describing HTTP APIs. Version 3.1, released in February 2021, introduced full JSON Schema compatibility and resolved long-standing structural inconsistencies. It is the foundation of the modern API economy — used by cloud providers, SaaS platforms, financial institutions, and government APIs as the canonical format for API contract documentation.
An OpenAPI specification functions simultaneously as human-readable documentation, machine-readable API contract, and the source of truth for code generation, testing, and client SDK generation. Organizations that maintain high-quality OpenAPI specifications reduce developer onboarding time, API support overhead, and integration errors — while creating documentation infrastructure that can be governed, versioned, and audited.
API title, version, description, contact information, and license documentation.
All API endpoints with HTTP methods, parameters, request bodies, responses, and security requirements.
Reusable schema definitions, response definitions, parameter definitions, and security scheme definitions.
Authentication documentation: OAuth 2.0, API key, HTTP Bearer, OpenID Connect.
API server URLs, environment definitions, and server variable documentation.
Webhook event documentation for asynchronous callback APIs.
Templates and implementation resources for OpenAPI Specification 3.1 are available through the ELDR Institute Knowledge Hub and via direct request.