Fern

Automated API documentation and idiomatic SDK generation platform for engineering teams.

About Fern

Fern is an API toolchain that automates the generation of developer portals and idiomatic SDKs from OpenAPI specifications or Fern’s own definition format. It is built for engineering teams who want to provide stripe-level developer experiences without manually maintaining client libraries and complex portal infrastructure.

Fern integrates directly into GitHub workflows, automatically updating documentation and publishing SDKs to package managers (like npm, PyPI, and Maven) whenever the API specification changes. This ensures that documentation, client libraries, and the backend API remain perfectly synchronized.

Key Features

Idiomatic SDK Generation: Generates native, typed client libraries in TypeScript, Python, Java, Go, and more.
Automated Docs Publishing: Generates beautiful, responsive API references and developer portals.
Docs-as-Code Configuration: Configures documentation layouts and content using code and markdown.
CI/CD Integration: Runs as a GitHub Action to automate SDK and docs deployment.
OpenAPI Compatibility: Imports existing OpenAPI specifications out of the box.
Snippet Generation: Automatically injects accurate SDK code snippets into the API documentation.

Pricing

Free: $0/month Includes up to 10 team members, 1 docs site, 1,000 pages, 2,000 page generations/month, and 250 AI credits/month. Includes custom domains, versioning, and PDF exports. (Special "Postman Free" tier extends this to 25 members and 500 AI credits).
Enterprise: Custom pricing Everything in Free, plus SSO, RBAC, multiple sites/repos, custom CSS/React components, dedicated infrastructure, and advanced analytics.
SDK Generation: Custom pricing SDK generation is priced separately under Enterprise/Custom terms and does not have a publicly published rate card.

Use Cases

Generating native SDKs for multiple languages
Automating API documentation deployments
Creating synchronized docs and client libraries
Upgrading from legacy OpenAPI generators

Pros & Cons

Pros:

Best-in-class, idiomatic SDK generation
Very generous Free tier (10 seats, custom domains included)
Seamless CI/CD automation

Cons:

Large functionality gap between the Free tier and the custom Enterprise tier
Heavily reliant on CI/CD configuration expertise

Integrations

GitHub, npm, PyPI, Maven, Go Modules

FAQ

Does Fern replace OpenAPI?

No, Fern can ingest your existing OpenAPI specification to generate documentation and SDKs, though it also offers its own Fern Definition language for advanced use cases.

What languages does Fern generate SDKs for?

Fern generates idiomatic SDKs for Node.js/TypeScript, Python, Java, Go, Ruby, C#, and PHP.

Are the generated SDKs idiomatic?

Yes, unlike older open-source generators, Fern is specifically designed to produce clean, strongly-typed, and human-readable code that feels native to the target language.

How is the documentation updated?

Fern runs in your CI/CD pipeline (e.g., GitHub Actions) and automatically regenerates and deploys your documentation whenever you push changes to your API definition.