Fern automates the two most time-consuming aspects of API development: SDK creation and documentation maintenance. Starting from an OpenAPI or Fern specification, the platform generates fully idiomatic client SDKs that feel hand-written — complete with proper type definitions, error handling, automatic retries with exponential backoff, pagination helpers, and streaming support. SDKs are generated for TypeScript, Python, Java, Go, Ruby, and C# with language-specific conventions respected throughout, producing code that API consumers can trust in production.
The documentation engine produces beautiful, interactive API references with request/response examples, authentication guides, and webhook documentation. Fern's AI-powered search assistant helps developers find relevant endpoints and examples using natural language queries. Documentation stays in sync with the API specification through CI/CD integration — when the spec changes, SDKs and docs are regenerated and published automatically. The platform supports custom domains, branding, and MDX-based content for supplementary guides.
Fern is used by API-first companies including Cohere, ElevenLabs, Merge, Flatfile, and others who need high-quality developer experience for their APIs. The platform offers a free tier for getting started and paid plans for teams needing advanced features. The open-source Fern compiler on GitHub handles specification parsing and code generation, while the hosted platform adds documentation hosting, SDK publishing, and collaboration features. For API teams, Fern eliminates the SDK and documentation maintenance burden that scales linearly with API surface area.
