Top OPENAPI3 GitHub Repositories & Tools (2026)

FastAPI framework, high performance, easy to learn, fast to code, ready for production

Detect breaking changes between OpenAPI 3.0/3.1 specs. Explainable Web UI, CLI and CI gate; local-first and deterministic, with optional AI summaries.

OpenAPI Generator allows generation of API client libraries (SDK generation), server stubs, documentation and configuration automatically given an OpenAPI Spec (v2, v3)

Examples and server integrations for generating the Swagger API Specification, which enables easy access to your REST API

OpenAPI based HTTP Client code generator

The open source, cloud native tool for API Mocking and Testing. Microcks is a Cloud Native Computing Foundation incubating project 🚀

😎 A list of awesome projects related to OpenAPI 3.0.x, curated by the community

A RESTful framework built on top of light-4j with both Swagger 2.0 and OpenAPI 3.0 supports

Open-source OpenAPI mock server with cloud hosting and local modes for development, testing, and CI. Generates realistic API responses from specs with latency simulation, error injection, proxy fallback, and request validation. Validated against 2,200+ real-world OpenAPI specs.