# Fern

Generate SDKs and docs from your API spec. Fern keeps your SDKs, documentation, and Model Context Protocol server in sync with one source of truth.

## What Fern does

- **SDKs** — Idiomatic client libraries in 9 languages (TypeScript, Python, Go, Java, C#, Ruby, PHP, Swift, Rust). Generated from your OpenAPI or AsyncAPI spec.
- **Docs** — Interactive API documentation, versioned and searchable. Beautiful out of the box, fully themeable.
- **MCP server** — Expose your API to Claude, Cursor, and other AI clients via the Model Context Protocol.
- **Ask Fern** — Conversational answers grounded in your docs and API reference.
- **llms.txt** — Auto-generated index and full-text Markdown for AI agents.

## Why teams pick Fern

- Single source of truth. Your spec is the input; SDKs, docs, and AI surfaces stay in sync.
- Idiomatic SDKs. Generated code reads like a human wrote it — strongly typed, paginated, retry-aware, OAuth-aware.
- Forward-compatible. SDKs handle unknown fields, deprecations, and additive changes without breaking old clients.
- Built for agents. MCP server, llms.txt, and clean Markdown variants of every page make the docs first-class for AI consumers.

## Customers

NVIDIA, Adobe, ElevenLabs, Twilio, Cohere, OpenRouter, Square, Deepgram, Frame, Payabli, Unleash, and others rely on Fern to power their developer experience.

## How it works

1. Bring your OpenAPI or AsyncAPI spec.
2. Configure Fern (one YAML file, sensible defaults).
3. Publish SDKs to package registries and docs to your domain.
4. Regenerate on every spec change — drift is impossible.

## Get started

- Start for free: <https://buildwithfern.com/book-demo>
- Book a demo: <https://buildwithfern.com/book-demo>
- Pricing: <https://buildwithfern.com/pricing>