Developer Tools

Fern

Turn your API spec into docs, SDKs, and CLI — with AI search and agent-friendly docs

buildwithfern.com

Verified API available Free tier

Quick facts
What is it	Turn your API spec into docs, SDKs, and CLI — with AI search and agent-friendly docs
Pricing	Freemium — from $200/mo
Free tier	Yes
Platform	Web Application
API	Yes
Best for	Building and documenting a public API for a service, Generating client libraries for multiple programming languages
Domain registered	2022

Data updated Aug. 1, 2026

What does Fern do?

Fern is a developer platform that takes your API definition (OpenAPI, GraphQL, AsyncAPI, or gRPC) and automatically generates professional documentation, client SDKs in multiple languages, and a command-line interface. It’s built for the AI era, which means it doesn’t just serve human developers — it also prepares your API for AI agents to consume. You get a beautiful docs site with a search bar, an AI chat assistant, and agent-friendly outputs like llms.txt and an MCP server.

How does it work? You define your API structure in a fern.yml file or import an existing OpenAPI spec. A single `fern generate` command then produces everything: a customizable documentation website with your branding, SDKs designed by language experts (TypeScript, Python, and more), and a CLI for terminal interactions. The docs include an AI-powered search that understands natural language questions, and a “Try it” button to make live API calls right from the browser. Fern also supports modern protocols, so you can document REST, WebSockets, and GraphQL endpoints in one place.

Fern is best for API-first companies, startups shipping new APIs, and developer experience teams that want to reduce the time between someone reading the docs and making their first API call. Real-world use cases include generating SDKs for a voice agent API (as shown on the homepage), publishing internal or external API documentation, and setting up an MCP server so AI agents can interact with your API programmatically. It’s a practical tool for anyone who needs to maintain a single source of truth for their API.

AI API Developer Tools Technical Specifications

#api development#api documentation#developer tools#openapi#sdk-generator#workflow automation

Key features

What makes it stand out

AI search that understands natural language questions about your API

Generate SDKs in TypeScript, Python, and more with one command

Interactive API docs with live 'Try it' endpoint testing

Agent-friendly outputs like llms.txt and MCP server for AI agents

Customizable documentation with your brand, colors, and layout

Who is Fern for?

Who benefits most from this tool

Building and documenting a public API for a service

Generating client libraries for multiple programming languages

Streamlining the internal API design and review process

Pricing

Free tier available — start without a credit card

Hobby

Free

2 team members
250 AI credits
Custom domain
Guides, API refs, and changelogs
API explorer
Web editor

Team

$200.0/month

$150.0/month billed yearly

Everything in Hobby, plus:

5 team members
1,000 AI credits
Custom subpath
Version and product switching
Password-protected docs
PDF exports

Enterprise

Custom

Everything in Team, plus:

Visitor authentication (JWT, SSO)
Role-based access control (RBAC)
Translated content
Self-hosting
Enterprise SSO
Dedicated Slack & Teams channel

Trust & presence

Domain Domain registered 2022

Gallery

Click any image to enlarge

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