llms.txt
# Fern Documentation
## Instructions for AI Agents
- For clean Markdown of any page, append `.md` to the page URL, or request the page URL with `Accept: text/markdown`
- Everything listed below is anonymous. No API key, token, or permission is needed to read this site.
- For the Fern Docs Public API (scoped documentation tokens, search credentials, current user), see https://buildwithfern.com/openapi.json
- For a complete documentation index, see https://buildwithfern.com/learn/llms.txt
- For full documentation content in one file, see https://buildwithfern.com/learn/llms-full.txt
- For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://buildwithfern.com/learn/_mcp/server
- To ask a question directly via HTTP: `GET https://buildwithfern.com/learn/api/fern-docs/ask?q=<your+question>&token=<token from llms.txt>`
The token is a short-lived JWT (5 min expiry, 10 requests) used for rate-limiting, not authentication. Fetch a fresh token from llms.txt when it expires.
## Pages
- [Fern: Docs, SDKs, and CLIs for your API](https://buildwithfern.com/index.md): Start with OpenAPI. Generate SDKs in multiple languages, interactive API documentation, and an agent-first CLI.
- [SDKs](https://buildwithfern.com/sdks.md): Generate idiomatic SDKs from your OpenAPI spec.
- [Docs](https://buildwithfern.com/docs.md): Beautiful, interactive documentation from your OpenAPI spec.
- [Fern CLI Generator: Ship a CLI for your API](https://buildwithfern.com/cli.md): Generate a branded command-line interface from your OpenAPI spec. Idiomatic for developers, JSON-first for agents, published to Homebrew, npm, and Scoop.
- [Pricing](https://buildwithfern.com/pricing.md): Pricing and feature comparisons for Fern's Free and Enterprise plans for API Docs and SDKs.
- [Customers](https://buildwithfern.com/customers.md): From startups to public companies, Fern powers your API developer experience.
- [Blog](https://buildwithfern.com/blog.md): Writing from the Fern team.
- [Careers](https://buildwithfern.com/careers.md): Join the Fern team. Building developer-first APIs in Brooklyn, NY.
- [Book a demo](https://buildwithfern.com/book-demo.md): Talk to the Fern team. Get a custom demo with a branded Docs site and SDK offerings, built specifically for your API.
- [Support](https://buildwithfern.com/support.md): Get help with Fern. Email support, open a GitHub issue, book a demo, or reach out in your dedicated Slack channel.
- [Trust center](https://buildwithfern.com/trust.md): Fern's trust center. Review our security posture and request access to compliance documentation, including SOC 2.
- [Fern Design](https://buildwithfern.com/design.md): The Fern design system: brand, color, typography, layout, shape, and motion tokens behind buildwithfern.com.
- [Make your Docs and SDKs agent-ready](https://buildwithfern.com/lp/agent-ready.md): Ship Docs and SDKs agents can actually read. Fern generates llms.txt, an MCP server, Ask Fern, clean markdown views, and typed SDKs so Claude, Cursor, and ChatGPT get the right answer the first time.
- [API Documentation Platform: interactive docs from your spec](https://buildwithfern.com/lp/api-docs.md): Generate interactive API documentation from your OpenAPI spec. Docs as code in Markdown with Git review, agent-ready with llms.txt and an MCP server built in.
- [Consolidate your API tech stack](https://buildwithfern.com/lp/consolidate-stack.md): Replace your docs platform, SDK generator, and reference portal with one. NVIDIA, Square, ElevenLabs, and Deepgram ship API docs and SDKs from Fern.
- [Your pipeline, not our dashboard](https://buildwithfern.com/lp/developer-tooling.md): Fern generates Docs and SDKs from one CLI that runs in your CI. Six spec formats in, nine SDK languages out, and every generator Apache-2.0 on GitHub.
- [Enterprise-grade SDKs and Docs](https://buildwithfern.com/lp/enterprise.md): Fern is the enterprise-grade SDK and Docs platform. SOC 2 Type II, self-hosted Docker deployment, SSO and SCIM, endpoint-level RBAC, and dedicated SDK engineers.
- [Fern vs Mintlify](https://buildwithfern.com/lp/fern-vs-mintlify.md): Evaluating Fern vs Mintlify? Compare SDK generation, self-hosting, access control, editor workflows, and agent readiness side by side.
- [Fern vs Speakeasy](https://buildwithfern.com/lp/fern-vs-speakeasy.md): Evaluating Fern vs Speakeasy? Compare languages, protocol coverage, generated code quality, docs, and deployment options side-by-side.
- [Fern vs Stoplight](https://buildwithfern.com/lp/fern-vs-stoplight.md): Evaluating Fern vs Stoplight? Compare SDK generation, agent readability, authoring workflows, self-hosting, and access control side by side.
- [Migrate from Speakeasy to Fern](https://buildwithfern.com/lp/leave-speakeasy.md): Teams choose Fern over Speakeasy for zero-dependency SDKs, multi-protocol generation, CLI-first workflows, production-ready docs, and on-premise deployment.
- [Migrate from Stainless to Fern](https://buildwithfern.com/lp/leave-stainless.md): Teams choose Fern over Stainless for 9+ languages, multi-protocol SDKs, CLI-first workflows, production-ready docs, and on-premise deployment.
- [SDK Generator: idiomatic SDKs in 9 languages](https://buildwithfern.com/lp/sdk-generator.md): Generate idiomatic SDKs from your OpenAPI spec in 9 languages, with retries, pagination, and tests built in. Open source generators, published to every registry on autopilot.
## Customer case studies
- [Solvimon builds its billing docs for the agents reading them](https://buildwithfern.com/customers/solvimon.md): How Solvimon moved off ReadMe to Fern Docs and made their billing documentation machine-readable, so AI agents now drive 90% of docs traffic while human readers still find the docs through organic search.
- [Auth0 ships identity features faster by generating SDKs with Fern](https://buildwithfern.com/customers/auth0.md): How Auth0 replaced hand-written SDKs with ones generated from a single OpenAPI spec.
- [Payabli builds best-in-class docs and SDKs for complex payment APIs with Fern](https://buildwithfern.com/customers/payabli.md): How Payabli migrated off Mintlify in three weeks and keeps 385 API examples and SDKs in eight languages in sync from a single source as their payment APIs change daily.
- [Deepgram unifies REST and WebSocket API documentation via Fern Docs](https://buildwithfern.com/customers/deepgram.md): How Deepgram consolidated REST (OpenAPI) and WebSocket (AsyncAPI 3.0) documentation into a single developer experience and opened contribution to PMs across the company.
- [Frame.io drives API adoption through streamlined docs and SDKs](https://buildwithfern.com/customers/frame.md): How Adobe's Frame.io team shipped SDKs alongside synced documentation and turned auth questions from 90% of their support load into self-serve answers.
- [Unleash scales AI-ready documentation with Fern Docs](https://buildwithfern.com/customers/unleash.md): How Unleash migrated 300+ pages off Docusaurus in two weeks and made every doc AI-ready as half their traffic shifted to LLM tools.
- [ElevenLabs scales voice AI infrastructure with Fern Docs & SDKs](https://buildwithfern.com/customers/elevenlabs.md): How ElevenLabs unified developer documentation and SDK generation on Fern as their API surface scaled to over a billion end users.
## Blog posts
- [Fern Docs sites are now static, and much faster](https://buildwithfern.com/post/static-docs.md): Part 2 of making Fern faster: every Docs site is now prebuilt as static pages, so pages load faster, local preview is quicker, and publishing never slows a site down.
- [We tested AI agents with and without an SDK. The SDK won.](https://buildwithfern.com/post/sdk-vs-raw-api-ai-agents-benchmark.md): Claude agents built a Square payments integration on raw HTTP, with an OpenAPI Generator SDK, and with Square's Fern-generated SDK. With Square's SDK, 11 of 12 integrations worked in production. With the other two setups, 2 of 12 did.
- [Kapa reviews, pricing, and alternatives (September 2026)](https://buildwithfern.com/post/kapa-reviews-pricing-alternatives.md): Kapa reviews, pricing, and alternatives: how kapa.ai's AI assistant works, what customers pay, and how Ask Fern, Inkeep, DocsBot, and a custom RAG build compare in September 2026.
- [Mintlify reviews, pricing, and alternatives (September 2026)](https://buildwithfern.com/post/mintlify-reviews-pricing-alternatives.md): Mintlify reviews, pricing, and alternatives: what the Pro plan and AI credits cost, where Mintlify fits, and how Fern, ReadMe, GitBook, and Docusaurus compare in September 2026.
- [Top custom code preservation tools for generated SDK maintenance (September 2026)](https://buildwithfern.com/post/custom-code-preservation-tools-sdk-maintenance.md): Compare the top custom code preservation tools for generated SDK maintenance, from ignore files to three-way merge patches, in September 2026.
- [Best Postman collection generation tools for developer testing (September 2026)](https://buildwithfern.com/post/postman-collection-generation-tools-developer-testing.md): Compare the best Postman collection generation tools for developer testing, from native import to contract-test generators and CI runners, in September 2026.
- [Automating PyPI releases: a CI/CD workflow for Python SDKs (September 2026)](https://buildwithfern.com/post/automating-pypi-releases-python-sdks.md): Automate Python SDK publishing with GitHub Actions: trusted publishing, computed versions, and the pre-upload test gate for PyPI releases in September 2026.
- [Speakeasy reviews, pricing, and alternatives (September 2026)](https://buildwithfern.com/post/speakeasy-reviews-pricing-alternatives.md): Speakeasy reviews, pricing, and alternatives: how its SDK generator compares to Fern, OpenAPI Generator, APIMatic, and Kiota in September 2026.
- [Generate idiomatic TypeScript clients from OpenAPI: complete guide (September 2026)](https://buildwithfern.com/post/generate-idiomatic-typescript-clients-from-openapi.md): Generate an idiomatic TypeScript client from OpenAPI: casing, unions, error shape, runtime targets, and the dependency budget. A complete guide for September 2026.
- [Multi-language SDK generation automation: complete guide (September 2026)](https://buildwithfern.com/post/multi-language-sdk-generation-automation.md): Multi-language SDK generation automation covers generation, versioning, testing, and publishing to every package registry. A complete guide for September 2026.
- [How we built Fern Agent](https://buildwithfern.com/post/building-fern-agent.md): How we built Fern Agent: why we persisted conversations before it had a single tool, taught it that valid markdown isn't valid Fern, and secured write access to customer docs before it shipped.
- [Handling breaking changes: automating semantic versioning for API SDKs (August 2026)](https://buildwithfern.com/post/automating-semantic-versioning-api-sdks-claude.md): Semantic versioning for API SDKs works when the bump is computed from the contract diff rather than the commit log. A CI playbook for August 2026.
- [How to generate Postman collections from OpenAPI automatically (August 2026)](https://buildwithfern.com/post/generate-postman-collections-from-openapi-claude.md): Learn how to generate a Postman collection from OpenAPI automatically in August 2026, and how to keep it regenerated in CI instead of maintained by hand.
- [One agent for your documentation](https://buildwithfern.com/post/fern-agent.md): Fern Agent is live in your Dashboard, Slack, and coding agent via MCP. It edits your markdown, restructures your nav, fixes your CSS, and answers from your real analytics, all from one conversation.
- [Top API authentication integration tools for OAuth and complex auth (August 2026)](https://buildwithfern.com/post/api-authentication-integration-tools-oauth-claude.md): Compare the top API authentication tools for OAuth integration and complex auth across authorization servers, gateways, and generated clients in August 2026.
- [Stopping schema drift: a guide to coupling SDKs with documentation (August 2026)](https://buildwithfern.com/post/stopping-schema-drift-coupling-sdks-documentation-claude.md): Documentation drift starts when SDKs and API docs are maintained apart from the schema. A guide to coupling them in one pipeline in August 2026.
- [Top automated package publishing platforms for SDK distribution (August 2026)](https://buildwithfern.com/post/automated-package-publishing-platforms-sdk-distribution.md): Compare the top automated package publishing platforms for SDK distribution, from npm publishing automation to PyPI automation, in August 2026.
- [How to migrate your developer portal to docs as code (August 2026)](https://buildwithfern.com/post/migrate-developer-portal-to-docs-as-code.md): Migrate to docs as code without breaking your developer portal: a dev portal migration playbook for content, URLs, CI, and cutover in August 2026.
- [How to write technical documentation: a complete guide (August 2026)](https://buildwithfern.com/post/how-to-write-technical-documentation.md): How to write technical documentation that stays accurate: audience mapping, a reusable template, generated reference, CI style checks, and examples in August 2026.
- [OpenAPI types: a guide to data types and formats (August 2026)](https://buildwithfern.com/post/openapi-types-data-types-formats.md): OpenAPI types explained: data types, formats, enum, oneOf, and constraints, and how each choice changes the SDKs and docs generated from your spec in August 2026.
- [How I ship Fern's marketing content using skills](https://buildwithfern.com/post/content-marketing-agents.md): I own marketing content at Fern: case studies, launch posts, engineering blogs, and the monthly changelog. Most of it starts as output from a Claude skill, and none of it ships without my edits.
- [AsyncAPI documentation generator: complete guide (July 2026)](https://buildwithfern.com/post/asyncapi-documentation-generator.md): How an AsyncAPI documentation generator works, which tools to evaluate, and how to document event-driven APIs and WebSocket channels in July 2026.
- [Best multi-protocol API development platforms supporting REST and gRPC (July 2026)](https://buildwithfern.com/post/multi-protocol-api-platforms-rest-grpc.md): Compare the best multi-protocol API platforms supporting REST and gRPC, with cross-protocol SDK generation and transcoding options evaluated in July 2026.
- [How I run six figures of paid ads](https://buildwithfern.com/post/paid-ads-agent.md): I set up an agent-friendly marketing engine that doubled demos, took 90% search impression share, and increased site traffic by 202%.
- [gRPC and REST unified documentation: a complete guide (July 2026)](https://buildwithfern.com/post/grpc-rest-unified-documentation.md): gRPC and REST unified documentation explained: how to document both protocols from one source of truth and generate SDKs in July 2026.
- [How to manage partner-only API documentation without building a second portal (July 2026)](https://buildwithfern.com/post/manage-partner-only-api-documentation.md): Partner API documentation without a second portal: use audience filtering and RBAC to gate partner-only API docs from a single source in July 2026.
- [How I perfected Midjourney prompts for our marketing assets](https://buildwithfern.com/post/midjourney-blog-art.md): The process of landing on a Midjourney prompt that generates beautiful, on-brand background imagery for our marketing assets.
- [From Fern customer to Fern sales engineer](https://buildwithfern.com/post/fernie-adi.md): Adi joined Fern as a sales engineer in June '26 after using Fern as a customer at a software analytics company. He walks through why he made the switch and the RBAC preview feature he shipped soon after.
- [API documentation for insurance carriers: a vendor comparison (July 2026)](https://buildwithfern.com/post/insurance-api-documentation-platforms-comparison.md): Compare insurance API documentation platforms in July 2026 on ACORD-scale specs, partner access controls, audit logging, and private deployment for carriers.
- [Reducing time-to-hello-world for enterprise partners (July 2026)](https://buildwithfern.com/post/reduce-time-to-hello-world-enterprise-partners.md): Reduce time to hello world for enterprise partners in July 2026 with generated SDKs, runnable docs, self-service access, and the dev onboarding metrics that prove it.
- [GitLab-integrated API documentation platforms for self-hosted enterprises (July 2026)](https://buildwithfern.com/post/gitlab-api-documentation-platforms-self-hosted.md): Compare GitLab API documentation platforms for self-hosted enterprises: GitLab self-managed integration, on-prem deployment, and spec-driven sync in July 2026.
- [What is an API CLI generator? A complete guide for developers (July 2026)](https://buildwithfern.com/post/what-is-an-api-cli-generator.md): An API CLI generator turns your OpenAPI spec into a command-line tool. Complete guide to how it works, benefits, and tradeoffs in July 2026.
- [How to build a CLI for your API without writing it from scratch (July 2026)](https://buildwithfern.com/post/how-to-build-a-cli-for-your-api.md): How to build a CLI for your API in July 2026: design commands, auth, and output, then generate the whole tool from your OpenAPI spec instead of hand-coding it.
- [OpenAPI Generator CLI vs Fern: what's the difference? (July 2026)](https://buildwithfern.com/post/openapi-generator-cli-vs-fern.md): Compare openapi-generator-cli vs Fern CLI in July 2026: template-based generation you maintain yourself versus idiomatic SDKs and synced docs from one spec.
- [Our largest docs sites now render ~6.4x faster](https://buildwithfern.com/post/faster-docs.md): Our docs platform used to store each entire site as a single monolithic JSON object. Here's why that fell apart, and how we rebuilt storage so a one-page edit only touches the one page.
- [CLI vs MCP: which API interface should you build first? (June 2026)](https://buildwithfern.com/post/cli-vs-mcp-which-api-interface-first.md): CLI vs MCP: Learn which API interface to build first for AI agents. Compare token costs, auth models, and workflows. June 2026 guide with code examples.
- [Why API first approach matters and what it means for development in 2026](https://buildwithfern.com/post/what-is-api-first-approach.md): Learn what an API first approach means, how it differs from code-first development, and why it matters for teams building APIs in June 2026.
- [When to use MCP vs a CLI for API access: a practical guide (June 2026)](https://buildwithfern.com/post/mcp-vs-cli-api-access.md): Learn when to use MCP vs a CLI for API access in June 2026. Compare agent-driven workflows with direct API calls to pick the right integration method.
- [SDK vs CLI vs MCP: choosing the right interface for your API (June 2026)](https://buildwithfern.com/post/sdk-vs-cli-vs-mcp-choosing-interface.md): Compare SDK, CLI, and MCP interfaces for your API. Learn which fits your workflow, token costs, and auth requirements. June 2026 analysis.
- [Why Fern takes a developer-first approach to SDK generation and API documentation June 2026](https://buildwithfern.com/post/fern-developer-first-sdk-generation-api-documentation.md): Learn why Fern takes a developer-first approach to SDK generation and API documentation in June 2026. Generate SDKs and docs from one spec automatically.
- [How to generate a CLI from your OpenAPI spec (June 2026)](https://buildwithfern.com/post/generate-cli-from-openapi-spec.md): Learn how to generate a CLI from your OpenAPI spec in June 2026. Keep commands synchronized with your API automatically without manual coding or drift.
- [How 2 designers and AI rebuilt Fern's marketing site](https://buildwithfern.com/post/building-fern-site.md): How we leveraged AI in our design process. We set the creative direction up front and refined the final details ourselves; AI h
