Fern
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.
Real signal across most facets with visible, nameable gaps — the contract exists but is thin, or the portal is good while governance and commercial terms are absent.
API Evangelist profiles Fern the way a machine reads it — 54 machine-readable artifacts across 1 API, pulled from the provider's own public surface and indexed so a developer, an analyst, or an AI agent can evaluate it against every other provider on the network.
Every provider in the network is reduced to the same set of machine-readable artifacts — OpenAPI contracts, event specifications, GraphQL schemas, runnable collections, pricing and rate-limit signals, security posture, OAuth scopes, and the agent surfaces (MCP servers and skills) that let software drive the API on its own. We profile them because the interface is the part of a company you can actually inspect: it is a truer signal of what a provider does than any marketing page. From those artifacts we compute the Kin Score — Fern scores 58.6/100 (developing), with a separate agent-readiness read of 18/100 (agent aware). The full breakdown is below, followed by every artifact we hold — each card links through to its machine-readable definition on apis.io.
Kin Score
This is the API Evangelist rating — a single, repeatable read computed from the artifacts on this page. Green fill is points earned; the red track is points possible, so every bar shows earned-versus-possible at a glance.
Kin Score
How this is scored →scored 2026-07-27 · rubric v0.5
How we profile Fern
Each block below is one kind of artifact we hold for Fern. For each we say what it is and why it earns a place in the profile, then list every one we've indexed — capped at two rows, scroll within the panel for the rest.
APIs 1
Each API is captured as its own OpenAPI definition — every operation, parameter, and response. This is the single most useful machine-readable description of what an API does, and it's what lets us score, lint, mock, and generate against it without asking the provider for anything.
Individual APIs this provider publishes, each with its own machine-readable definition.
Fern
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 d...
MCP Servers 1
Model Context Protocol servers expose these APIs directly to AI agents. We profile them because agent-native access is the fastest-growing way this provider's capabilities actually get used.
Model Context Protocol servers that expose these APIs to AI agents.
fern-mcp-server
MCP SERVERPricing Plans 1
Pricing is part of the interface. Machine-readable plans tell you what a tier costs and includes before you commit — one of the six things the Kin Score reads for commercial clarity.
Published pricing tiers and plan structures.
Fern Plans Pricing
PLANSRate Limits 1
Rate limits are the difference between a demo that works and a production integration that doesn't fall over. Publishing them is an operational-transparency signal — and a hard requirement for any agent that plans its own throughput.
Documented rate limits and quota policies.
Fern Rate Limits
RATE LIMITSFinOps 1
Cost, billing, and metering signals let a buyer model the financial operations of an API before it's live. We profile them for the same reason we profile pricing: the money is part of the contract.
Cost, billing, and metering signals for API financial operations.
Fern Finops
FINOPSFeatures 12
The notable capabilities this provider advertises, captured as structured features so they can be searched and compared instead of read one landing page at a time.
Notable capabilities this provider offers.
SDK Generation
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.
API Documentation
Auto-generate beautiful, branded API documentation with interactive API explorer, search, dark mode, SEO, and custom domain support.
Ask Fern
AI-powered in-docs search and chatbot that answers developer questions using your API docs, SDKs, and guides as context.
Fern Definition Language
Purpose-built API definition language as an alternative to OpenAPI for authoring API contracts.
llms.txt Generation
Auto-generated llms.txt markdown artifacts so LLMs and AI agents can consume documentation directly.
MCP Server
Hosted Model Context Protocol server that connects Claude, Cursor, and Windsurf to Ask Fern AI search and the Fern docs and SDK platform.
Agent Score
Open-source tool that rates documentation sites on their agent readiness across structure, semantics, and machine-readable content.
Fern Writer
AI-assisted documentation authoring inside the Fern docs platform.
Multi-Protocol Support
First-class support for OpenAPI (REST plus Webhooks), AsyncAPI (WebSockets), Protobuf (gRPC), and OpenRPC.
Versioning and Multi-Product
Built-in versioning, product switching, and multi-source aggregation across multiple APIs and product surfaces.
Self-Hosting
Enterprise self-hosting of the Fern docs platform inside a customer environment.
Visitor Authentication
JWT and SSO-gated docs for partner-only and internal documentation.
Scroll within the panel for all 12 ·
Semantic Vocabularies 1
JSON-LD contexts give the data shared meaning across APIs. We profile them because semantics are what let a machine reconcile 'customer' here with 'customer' somewhere else.
JSON-LD contexts and semantic vocabularies used across these APIs.
Fern Context
JSON-LDSpectral Rules 1
Governance rulesets we run against this provider's specs — the automated checks behind parts of the score. Profiling them makes the quality bar explicit and re-runnable, not a matter of opinion.
Fern API Rules
SPECTRALJSON Schema 4
Standalone JSON Schema definitions describe the data models behind the API. We profile them so the shapes are validatable on their own — useful long after a single request is forgotten.
Standalone JSON Schema definitions for this provider's data models.
Fern API Definition
JSON SCHEMAFern Docs Configuration
JSON SCHEMAFern MCP Tool Invocation
JSON SCHEMAFern SDK Generator
JSON SCHEMAJSON Structure 3
JSON Structure captures the data shapes in a form built for tooling — a complement to JSON Schema that keeps the model machine-legible.
JSON Structure definitions describing this provider's data shapes.
Fern Api Definition Structure
JSON STRUCTUREFern Docs Config Structure
JSON STRUCTUREFern Sdk Generator Structure
JSON STRUCTUREExamples 5
Real request and response payloads are what turn a spec from abstract into obvious — and they're one of the twelve things an agent needs to call an API correctly on the first try.
Example request and response payloads for these APIs.
Security Posture 1
Authentication, domain security, vulnerability disclosure, and trust-center signals — the evidence that a provider takes security seriously enough to document it. We profile it because you can't govern what you can't see.
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Use Cases 7
What developers actually build with this provider — captured so the catalogue answers 'what is this for', not just 'what does this expose'.
What developers build with this provider.
SDK Generation from OpenAPI
Transform OpenAPI specifications into idiomatic client libraries across nine programming languages with automated publishing to npm, PyPI, Maven Central, NuGet, and other regist...
Developer Documentation Hosting
Replace Docusaurus, Mintlify, GitBook, or ReadMe with a Fern-hosted docs site featuring custom branding and domain.
API-First Development
Define APIs in Fern Definition Language and generate server stubs, SDKs, and documentation from one source of truth.
SDK Maintenance Automation
Auto-update and re-publish SDKs each time an OpenAPI specification changes via GitHub Actions CI/CD.
Agent-Ready Documentation
Make docs consumable by LLMs and AI coding agents through llms.txt, MCP, and structured semantic content.
Multi-Protocol Reference Docs
Document REST plus WebSocket plus gRPC surfaces in a single unified developer experience.
Migration From Stainless, ReadMe, Mintlify, or GitBook
Migrate existing developer docs and SDK pipelines to Fern in days rather than quarters.
Scroll within the panel for all 7 ·
Integrations 15
Pre-built integrations with other platforms tell you where this provider already fits in a stack.
Pre-built integrations with other platforms and tools.
GitHub Actions
First-party GitHub Actions for SDK generation, OpenAPI sync, and CI/CD publishing workflows.
npm Registry
Automatic publishing of generated TypeScript and JavaScript SDKs.
PyPI
Automatic publishing of generated Python SDKs.
Maven Central
Automatic publishing of generated Java SDKs.
NuGet
Automatic publishing of generated C# SDKs.
RubyGems
Automatic publishing of generated Ruby SDKs.
Packagist
Automatic publishing of generated PHP SDKs.
Crates.io
Automatic publishing of generated Rust SDKs.
Swift Package Manager
Distribution of generated Swift SDKs.
Go Modules
Distribution of generated Go SDKs via versioned tags.
Postman
Native ingestion of Postman collections as a documentation and SDK source.
Anthropic Claude
MCP server integration so Claude Desktop and Claude Code can query Ask Fern AI and assist with Fern workflows.
Cursor
MCP integration plus llms.txt make Fern-generated docs first-class context for the Cursor IDE.
Windsurf
MCP server support for Windsurf's AI coding environment.
ChatGPT, Gemini, Microsoft Copilot
Documentation indexing and llms.txt artifacts so leading LLMs can answer questions grounded in customer docs.
Scroll within the panel for all 15 ·
Resources
Every other property we hold for Fern — documentation, portals, status pages, policies, and corporate surface — grouped by the job it does, following the integrator's arc from getting started to running in production.
Get Started 3
Portal, sign-up, and the first successful call
Documentation 2
Reference material describing how the API behaves
Agent Surfaces 1
MCP servers, agent skills, and machine-readable catalogs
Design & Contract 2
Pagination, idempotency, versioning, errors, and events
Build 5
SDKs, sample code, and the tooling you integrate with
Access & Security 3
Authentication, authorization, and security posture
Operate 3
Status, limits, changes, and where to get help
Commercial 5
Pricing, plans, and the legal terms of use
Company 3
The organization behind the API
Other 6
Properties that don't map to a standard resource type
← All providers · Data indexed from github.com/api-evangelist/fern · machine-readable index on apis.io