Fern

aid: fern
name: Fern
description: >-
  Fern is an SDK generation and documentation platform designed for the AI era.
  It transforms OpenAPI, AsyncAPI, Protobuf (gRPC), and OpenRPC specifications
  into idiomatic, production-ready SDKs across nine languages plus auto-generated,
  branded developer documentation, an AI-first CLI, llms.txt for agent
  discoverability, Ask Fern AI search, and an MCP server that connects Claude,
  Cursor, and Windsurf into the workflow. Engineering teams at ElevenLabs,
  Deepgram, Square, Webflow, Auth0, LaunchDarkly, Cohere, Pinecone, Cash App,
  and OpenRouter use Fern to deliver world-class developer experiences from a
  single source of truth.
image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
url: >-
  https://raw.githubusercontent.com/api-evangelist/fern/refs/heads/main/apis.yml
created: '2025-01-08'
modified: '2026-05-22'
specificationVersion: '0.19'
kind: contract
access: 3rd-Party
position: Consuming
tags:
  - Agent Ready
  - AI
  - API Definitions
  - AsyncAPI
  - Code Generation
  - Developer Experience
  - Developer Portal
  - Documentation
  - gRPC
  - llms.txt
  - MCP
  - OpenAPI
  - OpenRPC
  - Platform
  - Protobuf
  - SDKs
  - WebSockets
segments:
  - SDKs
  - Documentation
  - API Definitions
  - Developer Experience
  - Code Generation
  - Agent Ready
  - MCP
apis:
  - aid: fern:fern
    name: Fern
    description: >-
      Fern transforms a single API source of truth (OpenAPI, AsyncAPI, Protobuf,
      OpenRPC, or the Fern Definition Language) into type-safe SDKs in nine
      languages, branded interactive documentation with API explorer, an
      agent-first CLI, llms.txt artifacts, and an MCP server. The platform is
      positioned as Docs, SDKs, and CLIs designed for the AI era.
    humanURL: https://buildwithfern.com/
    tags:
      - Agent Ready
      - AI
      - API Definitions
      - AsyncAPI
      - Code Generation
      - Developer Experience
      - Documentation
      - gRPC
      - llms.txt
      - MCP
      - OpenAPI
      - OpenRPC
      - Platform
      - Protobuf
      - SDKs
      - WebSockets
    properties:
      - type: Documentation
        url: https://buildwithfern.com/learn
      - type: GettingStarted
        url: https://buildwithfern.com/learn/docs/getting-started/overview
      - type: SDK
        url: https://buildwithfern.com/learn/sdks/overview/introduction
      - type: APIReference
        url: https://buildwithfern.com/learn/docs/api-references/generate-api-ref
      - type: CLI
        url: https://buildwithfern.com/learn/cli-reference/overview
      - type: MCPServer
        url: https://github.com/fern-api/fern-mcp-server
      - type: Changelog
        url: https://buildwithfern.com/learn/changelog
      - type: Showcase
        url: https://www.buildwithfern.com/showcase
common:
  - type: GitHubOrganization
    url: https://github.com/fern-api
  - type: GitHubRepository
    url: https://github.com/fern-api/fern
  - type: Branding
    url: https://brandfetch.com/buildwithfern.com
  - type: Documentation
    url: https://buildwithfern.com/learn
  - type: CLI
    url: https://buildwithfern.com/learn/cli-reference/overview
  - type: Customers
    url: https://www.buildwithfern.com/showcase
  - type: Pricing
    url: https://www.buildwithfern.com/pricing
  - type: Blog
    url: https://www.buildwithfern.com/blog
  - type: Support
    url: https://buildwithfern.com/learn#get-support
  - type: PrivacyPolicy
    url: https://www.buildwithfern.com/privacy-policy
  - type: TermsOfService
    url: https://www.buildwithfern.com/terms-of-service
  - type: GettingStarted
    url: https://buildwithfern.com/learn/docs/getting-started/quickstart
  - type: Login
    url: https://dashboard.buildwithfern.com/login
  - type: SignUp
    url: https://dashboard.buildwithfern.com/login
  - type: X
    url: https://x.com/buildwithfern
  - type: LinkedIn
    url: https://www.linkedin.com/company/buildwithfern
  - type: TrustCenter
    url: https://security.buildwithfern.com/
  - type: MCPServer
    url: https://github.com/fern-api/fern-mcp-server
  - type: AgentReadinessScore
    url: https://github.com/fern-api/agent-score
  - type: Changelog
    url: https://buildwithfern.com/learn/changelog
  - type: Plans
    url: https://raw.githubusercontent.com/api-evangelist/fern/refs/heads/main/plans/fern-plans-pricing.yml
  - type: RateLimits
    url: https://raw.githubusercontent.com/api-evangelist/fern/refs/heads/main/rate-limits/fern-rate-limits.yml
  - type: FinOps
    url: https://raw.githubusercontent.com/api-evangelist/fern/refs/heads/main/finops/fern-finops.yml
  - type: Capabilities
    url: https://github.com/api-evangelist/fern/tree/main/capabilities
  - type: JSONSchema
    url: https://github.com/api-evangelist/fern/tree/main/json-schema
  - type: JSONLD
    url: https://raw.githubusercontent.com/api-evangelist/fern/refs/heads/main/json-ld/fern-context.jsonld
  - type: Vocabulary
    url: https://raw.githubusercontent.com/api-evangelist/fern/refs/heads/main/vocabulary/fern-vocabulary.yml
  - type: Features
    data:
      - name: SDK Generation
        description: Generate production-ready, type-safe SDKs in TypeScript, Python, Go, Java, C#, PHP, Ruby, Swift, and Rust from OpenAPI, AsyncAPI, Protobuf, or the Fern Definition Language.
      - name: API Documentation
        description: Auto-generate beautiful, branded API documentation with interactive API explorer, search, dark mode, SEO, and custom domain support.
      - name: Ask Fern
        description: AI-powered in-docs search and chatbot that answers developer questions using your API docs, SDKs, and guides as context.
      - name: Fern Definition Language
        description: Purpose-built API definition language as an alternative to OpenAPI for authoring API contracts.
      - name: llms.txt Generation
        description: Auto-generated llms.txt markdown artifacts so LLMs and AI agents can consume documentation directly.
      - name: MCP Server
        description: Hosted Model Context Protocol server that connects Claude, Cursor, and Windsurf to Ask Fern AI search and the Fern docs and SDK platform.
      - name: Agent Score
        description: Open-source tool that rates documentation sites on their agent readiness across structure, semantics, and machine-readable content.
      - name: Fern Writer
        description: AI-assisted documentation authoring inside the Fern docs platform.
      - name: Multi-Protocol Support
        description: First-class support for OpenAPI (REST plus Webhooks), AsyncAPI (WebSockets), Protobuf (gRPC), and OpenRPC.
      - name: Versioning and Multi-Product
        description: Built-in versioning, product switching, and multi-source aggregation across multiple APIs and product surfaces.
      - name: Self-Hosting
        description: Enterprise self-hosting of the Fern docs platform inside a customer environment.
      - name: Visitor Authentication
        description: JWT and SSO-gated docs for partner-only and internal documentation.
  - type: UseCases
    data:
      - name: SDK Generation from OpenAPI
        description: Transform OpenAPI specifications into idiomatic client libraries across nine programming languages with automated publishing to npm, PyPI, Maven Central, NuGet, and other registries.
      - name: Developer Documentation Hosting
        description: Replace Docusaurus, Mintlify, GitBook, or ReadMe with a Fern-hosted docs site featuring custom branding and domain.
      - name: API-First Development
        description: Define APIs in Fern Definition Language and generate server stubs, SDKs, and documentation from one source of truth.
      - name: SDK Maintenance Automation
        description: Auto-update and re-publish SDKs each time an OpenAPI specification changes via GitHub Actions CI/CD.
      - name: Agent-Ready Documentation
        description: Make docs consumable by LLMs and AI coding agents through llms.txt, MCP, and structured semantic content.
      - name: Multi-Protocol Reference Docs
        description: Document REST plus WebSocket plus gRPC surfaces in a single unified developer experience.
      - name: Migration From Stainless, ReadMe, Mintlify, or GitBook
        description: Migrate existing developer docs and SDK pipelines to Fern in days rather than quarters.
  - type: Integrations
    data:
      - name: GitHub Actions
        description: First-party GitHub Actions for SDK generation, OpenAPI sync, and CI/CD publishing workflows.
      - name: npm Registry
        description: Automatic publishing of generated TypeScript and JavaScript SDKs.
      - name: PyPI
        description: Automatic publishing of generated Python SDKs.
      - name: Maven Central
        description: Automatic publishing of generated Java SDKs.
      - name: NuGet
        description: Automatic publishing of generated C# SDKs.
      - name: RubyGems
        description: Automatic publishing of generated Ruby SDKs.
      - name: Packagist
        description: Automatic publishing of generated PHP SDKs.
      - name: Crates.io
        description: Automatic publishing of generated Rust SDKs.
      - name: Swift Package Manager
        description: Distribution of generated Swift SDKs.
      - name: Go Modules
        description: Distribution of generated Go SDKs via versioned tags.
      - name: Postman
        description: Native ingestion of Postman collections as a documentation and SDK source.
      - name: Anthropic Claude
        description: MCP server integration so Claude Desktop and Claude Code can query Ask Fern AI and assist with Fern workflows.
      - name: Cursor
        description: MCP integration plus llms.txt make Fern-generated docs first-class context for the Cursor IDE.
      - name: Windsurf
        description: MCP server support for Windsurf's AI coding environment.
      - name: ChatGPT, Gemini, Microsoft Copilot
        description: Documentation indexing and llms.txt artifacts so leading LLMs can answer questions grounded in customer docs.
  - type: Partnerships
    data:
      - name: Anthropic
        description: Claude integration via the fern-mcp-server and Ask Fern AI knowledge surface.
      - name: Cursor
        description: Cursor MCP integration and llms.txt-driven context for AI-assisted coding against Fern-documented APIs.
      - name: Windsurf
        description: MCP integration with Codeium Windsurf.
      - name: Postman
        description: Joint blog series and integration delivering world-class developer experiences alongside Postman collections.
  - type: SDK
    data:
      - name: TypeScript SDK Generator
        description: Generates idiomatic TypeScript and JavaScript SDKs with full type safety, published to npm.
      - name: Python SDK Generator
        description: Generates idiomatic Python SDKs with Pydantic models, published to PyPI.
      - name: Go SDK Generator
        description: Generates idiomatic Go SDKs published as Go modules.
      - name: Java SDK Generator
        description: Generates idiomatic Java SDKs published to Maven Central.
      - name: C# SDK Generator
        description: Generates idiomatic C# SDKs published to NuGet.
      - name: PHP SDK Generator
        description: Generates idiomatic PHP SDKs published to Packagist.
      - name: Ruby SDK Generator
        description: Generates idiomatic Ruby SDKs published to RubyGems.
      - name: Swift SDK Generator
        description: Generates idiomatic Swift SDKs distributed via Swift Package Manager.
      - name: Rust SDK Generator
        description: Generates idiomatic Rust SDKs published to crates.io.
  - type: GitHubRepositories
    data:
      - name: fern
        description: Core platform. Input OpenAPI, output SDKs and docs. TypeScript, Apache-2.0, 3.6k+ stars, 170+ contributors.
        url: https://github.com/fern-api/fern
      - name: fern-mcp-server
        description: Model Context Protocol server exposing the ask_fern_ai tool to Claude, Cursor, and Windsurf via stdio and an HTTP endpoint.
        url: https://github.com/fern-api/fern-mcp-server
      - name: agent-score
        description: Rates docs sites on their agent readiness.
        url: https://github.com/fern-api/agent-score
      - name: docs-starter
        description: Starter template to publish docs from OpenAPI plus MDX.
        url: https://github.com/fern-api/docs-starter
      - name: docs-starter-fern-definition
        description: Starter template to publish docs from a Fern Definition.
        url: https://github.com/fern-api/docs-starter-fern-definition
      - name: sdk-starter
        description: Starter template for generating SDKs in TypeScript, Python, Go, Java, C#, PHP, and Ruby.
        url: https://github.com/fern-api/sdk-starter
      - name: sync-openapi
        description: GitHub Action that syncs OpenAPI specs to a Fern configuration.
        url: https://github.com/fern-api/sync-openapi
      - name: setup-fern-cli
        description: GitHub Action that installs the Fern CLI into a workflow via npm.
        url: https://github.com/fern-api/setup-fern-cli
      - name: actions
        description: Reusable Fern GitHub Actions for SDK and docs workflows.
        url: https://github.com/fern-api/actions
      - name: docs
        description: The Fern public documentation site, built with Fern.
        url: https://github.com/fern-api/docs
      - name: docs-templates
        description: Template collection for Fern documentation projects.
        url: https://github.com/fern-api/docs-templates
      - name: docs-examples
        description: Example Fern docs configurations.
        url: https://github.com/fern-api/docs-examples
      - name: docs-custom-js-example
        description: Example Fern docs site with custom headers and footers.
        url: https://github.com/fern-api/docs-custom-js-example
      - name: docs-site-sync
        description: Chrome extension for side-by-side comparison of old and new documentation sites during migration.
        url: https://github.com/fern-api/docs-site-sync
      - name: migration-checker
        description: Automated analysis tool for comparing old and new documentation sites during migration.
        url: https://github.com/fern-api/migration-checker
      - name: fastapi-starter
        description: Starter repo for FastAPI plus React using Fern.
        url: https://github.com/fern-api/fastapi-starter
      - name: express-starter
        description: Starter repo for Express using Fern.
        url: https://github.com/fern-api/express-starter
      - name: spring-starter
        description: Starter repo for Java Spring using Fern.
        url: https://github.com/fern-api/spring-starter
      - name: generator-cli-go
        description: Go library to invoke the Fern generator CLI.
        url: https://github.com/fern-api/generator-cli-go
      - name: generator-exec-go
        description: Go library for progress updates between the Go generator and Fern's remote generation server.
        url: https://github.com/fern-api/generator-exec-go
      - name: ir-go
        description: Go bindings for the Fern Intermediate Representation.
        url: https://github.com/fern-api/ir-go
      - name: protoc-gen-openapi
        description: A protoc plugin that compiles Protobuf services into OpenAPI for downstream Fern generation.
        url: https://github.com/fern-api/protoc-gen-openapi
      - name: sphinx-autodoc2-fern
        description: CLI that auto-generates Fern markdown API documentation for Python packages.
        url: https://github.com/fern-api/sphinx-autodoc2-fern
      - name: swift-sdk-comparison
        description: Reference comparison of Swift SDKs across different SDK generators.
        url: https://github.com/fern-api/swift-sdk-comparison
      - name: incident-node
        description: TypeScript SDK for the Incident.io public API, generated by Fern.
        url: https://github.com/fern-api/incident-node
      - name: incident-python
        description: Python SDK for the Incident.io public API, generated by Fern.
        url: https://github.com/fern-api/incident-python
      - name: make-unity-sdk
        description: CLI that converts a generated C# SDK into a Unity C# SDK.
        url: https://github.com/fern-api/make-unity-sdk
  - type: Customers
    data:
      - name: ElevenLabs
        description: Unified docs and SDKs on Fern at over one billion end users.
      - name: Deepgram
        description: Consolidated REST plus WebSocket documentation into a single developer experience.
      - name: OpenRouter
        description: Rebuilt docs platform around agent-native workflows, automated writing, and AI search.
      - name: Square
        description: SDKs across multiple languages generated by Fern.
      - name: Webflow
        description: SDKs across multiple languages generated by Fern.
      - name: Auth0
        description: SDKs and docs generated by Fern.
      - name: LaunchDarkly
        description: SDKs generated by Fern.
      - name: Cohere
        description: SDKs for AI inference APIs generated by Fern.
      - name: Pinecone
        description: SDKs for the vector database generated by Fern.
      - name: AssemblyAI
        description: SDKs generated by Fern.
      - name: Candid Health
        description: SDKs generated by Fern.
      - name: Merge
        description: SDKs and docs generated by Fern.
      - name: Vapi
        description: SDKs generated by Fern.
      - name: Flatfile
        description: SDKs generated by Fern.
      - name: Payabli
        description: Migrated from Mintlify in three weeks and built interactive developer tools on Fern.
      - name: Unleash
        description: Migrated 300+ pages off Docusaurus in two weeks and made every doc AI-ready.
      - name: Frame.io
        description: Turned auth questions from 90% of support load into self-serve answers on Fern.
      - name: Cash App
        description: Hosts developer docs on Fern.
      - name: Clearpay
        description: Hosts developer docs on Fern.
      - name: ID.me
        description: Hosts developer docs on Fern.
      - name: You.com
        description: Hosts developer docs on Fern.
      - name: Persona
        description: Hosts developer docs on Fern.
      - name: Instabase
        description: Hosts developer docs on Fern.
      - name: Chainalysis
        description: Hosts developer docs on Fern.
      - name: Ada
        description: Hosts developer docs on Fern.
      - name: Nominal
        description: Hosts developer docs on Fern.
      - name: Babel Street
        description: Hosts developer docs on Fern.
      - name: Beehiiv
        description: Hosts developer docs on Fern.
  - type: Compliance
    data:
      - name: SOC 2
        description: SOC 2 reported via the Fern Trust Center.
      - name: 21 CFR Part 11
        description: Healthcare and pharmaceutical regulatory compliance reported via the Trust Center.
      - name: SSO and SAML and OIDC
        description: Enterprise SSO available on the Enterprise plan.
      - name: Visitor Authentication
        description: JWT-based visitor authentication for partner and internal docs on Enterprise.
      - name: Self-Hosting
        description: Self-hosted deployment available on the Enterprise plan.
maintainers:
  - FN: Kin Lane
    email: [email protected]