OpenAPI Initiative

The OpenAPI Initiative is a Linux Foundation project that maintains the OpenAPI Specification, recognized as the world's most widely used API description standard for describing HTTP APIs. The specification provides a formal, vendor-neutral standard that allows developers to understand how an API works, how sequences of APIs work together, generate client code automatically across dozens of programming languages, create test suites from the contract, apply design standards through linting rules, and produce interactive documentation without writing manual prose. The initiative maintains three specifications. The core OpenAPI Specification, currently at version 3.1.1 released as an Internet Engineering Task Force Internet-Draft, defines a standard, programming-language-agnostic interface description for REST APIs using JSON Schema Draft 2020-12 for data validation. The Arazzo Specification, introduced in 2024 at version 1.0, describes sequences of API calls and workflows, enabling the definition of end-to-end business processes that span multiple endpoints with conditional branching, input and output mapping, and step dependencies. The Overlays Specification provides a mechanism for applying transformations to API descriptions without modifying the original source document, useful for adding documentation, filtering endpoints for specific consumers, and enriching legacy API definitions. The ecosystem includes hundreds of tools for code generation, testing, mocking, documentation, and governance from vendors including Swagger, Postman, Stoplight, SmartBear, Redocly, APIMatic, and Kong. The initiative hosts the annual DeveloperWeek OpenAPI Summit and offers the OpenAPI Fundamentals training course. Corporate members include Google, Microsoft, IBM, SAP, Salesforce, Restlet, and SmartBear. Copyright 2026 The Linux Foundation.