openAPI

OpenAPI is a specification for describing RESTful APIs in a machine-readable format. It enables developers, tools, and services to understand an API’s capabilities without access to source code, supporting automated documentation, testing, validation, and client generation.

The project originated as the Swagger Specification, created by Tony Tam in 2010. It gained broad adoption and was later donated to the Linux Foundation in 2016, where it was rebranded under the OpenAPI Initiative as the OpenAPI Specification. The OpenAPI Specification is the ongoing standard used by many organizations to describe their APIs, with the 3.x series being the current major version and 2.0 commonly referred to as Swagger 2.0.

OpenAPI documents describe the structure and behavior of an API. They are written in YAML or JSON and detail information such as paths, HTTP methods, parameters, request bodies, responses, authentication methods, and metadata. The specification supports reusable components like schemas, parameters, responses, and headers, enabling consistent definitions across an API surface. It also supports advanced features such as request and response examples, callbacks, and links in the 3.x versions.

Usage and tooling have grown around OpenAPI. The specification is used to generate interactive documentation (for example, via UI tools), create client SDKs and server stubs, perform contract testing, and enable API gateways and gateways’ configuration. It serves as a common contract that can be consumed by a wide range of development, testing, and deployment tools.

Governance and ecosystem: OpenAPI is maintained by the OpenAPI Initiative, a collaborative, vendor-neutral effort under the Linux Foundation. It has broad industry support and a large ecosystem of editors, validators, and generators.