Stainless
Accepts an OpenAPI spec and produces high-quality, idiomatic SDKs that feel hand-written across TypeScript, Python, Go, Java, Kotlin, Ruby, PHP, and C#. GitHub integration auto-regenerates SDKs when the spec changes. The team behind OpenAI, Anthropic, Cloudflare, and Meta's official SDKs.
Swagger / OpenAPI
Swagger UI is the canonical open-source renderer for interactive API documentation from OpenAPI specs, with 28k+ GitHub stars. SwaggerHub adds collaborative API design, versioning, and governance at scale. The de facto standard for REST API specification across the industry.