What is Fern?
Fern is a comprehensive developer experience platform that transforms API specifications into production-ready software development kits (SDKs) and interactive documentation. The platform supports various specification formats including OpenAPI, AsyncAPI, OpenRPC, gRPC, and its own Fern Definition format, allowing teams to start with their existing API definitions.
The system generates idiomatic SDKs in TypeScript, Python, Go, Java, Ruby, C#, and PHP, with Swift and Rust support coming soon. These SDKs include strong typing, inlined documentation, intuitive error handling, and support for advanced features like OAuth 2.0 authentication, server-sent events, auto-pagination, and polymorphism. The documentation platform creates SEO-optimized sites with API explorers, changelogs, guides, and landing pages that can be customized to match brand identity.
Features
- SDK Generation: Automatically generates idiomatic SDKs in TypeScript, Python, Go, Java, Ruby, C#, and PHP with strong typing and inlined documentation
- Interactive Documentation: Creates SEO-optimized API documentation sites with API explorers, guides, and changelogs
- Multiple Specification Support: Works with OpenAPI, AsyncAPI, OpenRPC, gRPC, and Fern Definition formats
- Advanced Authentication: Supports OAuth 2.0, basic authentication, bearer tokens, API keys, HMAC, and digest authentication
- Real-time Features: Includes server-sent events, WebSockets, and webhook verification capabilities
- Custom Code Integration: Allows extending generated SDKs with custom logic and dependencies without overwriting on regeneration
- Automated Publishing: Semantically versions and publishes packages to registries like npm, PyPI, and Maven
- AI Features: Includes AI search, AI writing agent, AI translations, and AI-generated code examples
Use Cases
- Generating client libraries for REST APIs in multiple programming languages
- Creating interactive API documentation portals for developer onboarding
- Automating SDK maintenance and updates as APIs evolve
- Building developer portals with API explorers and testing capabilities
- Providing real-time API documentation for WebSocket and server-sent event APIs
- Creating white-labeled documentation sites that match company branding
- Generating code snippets and examples for API endpoints
- Managing multiple API versions and products in a unified developer portal
FAQs
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What programming languages does Fern support for SDK generation?
Fern supports TypeScript, Python, Go, Java, Ruby, C#, and PHP for SDK generation, with Swift and Rust support coming soon. -
Can I customize the generated SDKs with my own code?
Yes, you can extend the generated SDKs with custom logic and dependencies, and your custom code won't be overwritten during regeneration. -
What API specification formats does Fern support?
Fern supports OpenAPI, AsyncAPI, OpenRPC, gRPC, and its own Fern Definition format for generating SDKs and documentation. -
Does Fern only generate API documentation or does it include other features?
Fern provides comprehensive developer documentation including guides, API references, changelogs, landing pages, and API explorers, not just basic API documentation. -
What AI features does Fern offer?
Fern includes AI search for documentation, an AI writing agent that drafts documentation updates, AI translations for multiple languages, and AI-generated code examples.
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Fern Uptime Monitor
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