OpenAPI Generator
The most widely adopted open-source code generator forked from Swagger Codegen. Given an OpenAPI spec, generates API client SDKs, server stubs, and documentation for 50+ languages and frameworks. 26k+ GitHub stars, 600k weekly NPM downloads, and 30M Docker pulls.
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.