Products
Elevate your developer experience
Start with Docs, SDKs, or both — it’s your choice.
Instant Docs and SDKs for your API
Start with an API spec. Generate SDKs in multiple languages and interactive API documentation tailored to your brand.
SDK Generation
SDKs that are designed by language experts
Every generated SDK respects the idioms of the language, contains strong types, inlined docs, and intuitive error handling.
Check out live SDKs built with Fern
Check out live SDKs built with Fern
We evaluated several SDK generators and Fern stood out for its clean, language-native, and thoughtfully architected code.
The Fern team partnered with us every step of the way including OpenAPI improvements, alpha releases and launch announcements.
John Fellman
Head of Engineering, Developer Platform
$600k
saved in engineer salaries
How SDK Generation Works
Just run fern generate
Fern generates and publishes client libraries, so you can focus on building the API.
1
Import your API spec
Start with OpenAPI, AsyncAPI, OpenRPC, gRPC, or our simpler Fern Definition format.
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2
Select languages to generate
We support TypeScript, Python, Go, Java, Ruby, C# & PHP.
Swift & Rust coming soon.
3
Add custom code
Extend the generated client with utility functions and custom logic.
Your changes won’t be overwritten on re-generation.
4
Publish packages
Fern semantically versions and publishes packages to each registry (e.g. npm, pypi, maven)
composer require your-company/your-company-php
> dotnet add package YourCompany.Net --version 1.0.0
gem install your_company
compile "com.your-company:java-sdk:1.0.0"
go get github.com/your-company/go-sdk
pip install your-company
npm install your-company
SDK Features
Every feature you need, built-in
Fern SDKs support OAuth 2.0, server-sent events, auto-pagination and more.
Automatic updates via CI/CD
Use the Fern CLI to generate SDKs as part of your release process.
OAuth 2.0
Handle OAuth 2.0 authentication seamlessly with automatic token management and refresh.
Server-sent events
Stream real-time updates effortlessly with built-in SSE support.
Auto pagination
Automatically iterate through paginated data with built-in pagination helpers.
Polymorphism (Unions)
Handle complex polymorphic data with native type safety in every language.
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Audiences
Filter your API definition to the endpoints and properties you want included in your SDK.
Multipart form uploads
Seamlessly handle multipart uploads with built-in utilities for streaming binary data and MIME types.
Retries with exponential backoff
Automatically retry failed requests and maximize the uptime of your API.
Idempotency headers
Send idempotency headers to ensure safe retries for sensitive operations (e.g. sending payments).
Code snippets over API
Fetch SDK code samples from our API and embed them in your application.
Dependency vulnerability scanning
Fern adheres to an SLA to detect and remediate vulnerable dependencies.
We partnered with Fern for SDKs, and after seeing their docs platform, it was a no-brainer to expand.
Vic Plummer
Dev Content Lead at
Built
with
Docs Features
Everything you need to impress your users
Stunning by default, easy to update, and designed to convert.
Docs as code
Use git to version and release changes to your documentation.
SEO optimized
Fern uses industry best practices to make your website fast and SEO optimized to rank.
Preview deployments
Preview changes to your documentation with a unique URL for each pull request.
API key injection
Automatically populate API keys so that users can instantly make API calls and see realistic responses.
Access control (RBAC)
Assign role-based permissions and configure what content a user can access.
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Federated authentication
Secure your documentation behind auth. Fern supports SSO, OAuth, and username + password.
Versioning
Document and manage multiple versions of your product or API to support users across different releases.
WebSockets
Document your WebSocket send and receive events with an AsyncAPI spec.
Interact with the WebSocket via an API Explorer that lets you establish live connections.
Component library
Leverage prebuilt components like cards, accordions, tabs, and code blocks.
Customize with JavaScript and CSS
Customize your docs with JavaScript and CSS to match your brand identity and extend functionality.
Bring your own React component
Build custom React components and embed them in your docs.
AI chat
Interact with an AI assistant trained on your docs to quickly find answers and troubleshoot issues.
/llms.txt
Serve an llms.txt with no extra effort, allowing agents to understand the capabilities of your product.
Built with
Fern automated SDK maintenance, allowing us to support all popular programming languages without needing dedicated engineering resources. Working with the Fern team is like having 'McKinsey for APIs' -- they bring expert-level guidance in OpenAPI and SDK design.
Liz Moy
Senior Developer Relations Engineer
Partnering with Fern, we went from 1 SDK → 4 SDKs and are set up to offer whatever language developers ask for next. Fern also generates our documentation website that perfectly matches Cohere's unique brand identity.
Billy Trend
Developer Relations Engineer
2 engineers
time freed up annually
The Fern Definition is absolutely fantastic. Compared to OpenAPI, it's more ergonomic and comes with powerful capabilities - you can organize endpoints by resource, import types across files, and represent complex APIs like server sent events and websockets.
Kabir Goel
Founding Engineer
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Fern is a mission-critical part of Candid's API. Keeping our docs, SDKs, and server implementation in sync was a nightmare. Fern enabled us to adopt API-first development — our engineers update the spec, run fern generate, and everything stays perfectly aligned.
Steve Yazicioglu
Head of Engineering
