Fern

Fern is a platform that builds API documentation, client SDKs and a command line tool from one API definition. It starts from an OpenAPI spec and produces the parts developers usually write by hand.

Fern creates a documentation website with an API reference, a changelog and search. It also generates type-safe SDKs in several languages, so developers can call your API from their own code. A CLI lets people interact with the API from the terminal. The docs site can include an MCP server, llms.txt and AI search, which helps agents find and use the content. The company says the code it generates is designed by language experts, and the CLI is open source under the Apache 2.0 license on GitHub.

• Host API docs with search, a reference and a changelog
• Generate type-safe SDKs in many languages
• Start from an OpenAPI spec
• Call your API from the terminal with a CLI
• Publish llms.txt and an MCP server for agents

API teams that want polished documentation and SDKs without maintaining them by hand will find it useful. Developer relations teams can also use the docs site and the agent features to reach more developers.

The site says you can start for free, and it offers a demo for larger teams. Paid plans are listed on the pricing page, so check there for limits that apply to your project. Because the output is generated from your spec, the quality of the API definition matters more than the tooling itself.