Fern

Fern, now "a Postman company" based in Brooklyn, generates documentation, SDKs, and CLI tools from API specifications, used by 8,000+ customers including ElevenLabs and Auth0, reporting 74,000+ docs read by AI agents and 13,000+ SDKs generated. It builds customizable documentation websites with a built-in AI chat ("Ask Fern"), auto-generates client libraries across multiple languages from a single spec, provides a CLI for terminal-based API interaction, supports REST, WebSockets, GraphQL, AsyncAPI, and gRPC, and includes AI-native features like llms.txt generation and MCP server integration — plus enterprise capabilities (SAML/OIDC, multi-source docs, self-hosting, localization) and direct Postman collection generation. A free tier lets you start; enterprise options exist for larger teams, with exact pricing on a separate page. Good fit for an API-first company that wants documentation, SDKs, and llms.txt/MCP support all generated automatically from one API specification, rather than maintained by hand across separate tools.