Fern review: generate type-safe SDKs and API docs from an OpenAPI spec. Pricing, key features, and how it compares to Mintlify, Stainless, and ReadMe.
Category
Developer Tools
Pricing
Freemium, from Free
Verified
Not yet
Last updated
July 18, 2026
Founded
2022
Headquarters
Brooklyn, New York, United States
Free PlanWeb AppAPIAIFreemium
Overview
Fern is a developer platform that turns a single API specification, such as an OpenAPI or AsyncAPI document, into type-safe client SDKs across multiple programming languages plus a matching API documentation website, so API-first companies do not have to hand-build and separately maintain both.
Founded in 2022 in Brooklyn and grown through Y Combinator, Fern was acquired by Postman in January 2026 and now continues operating as an independent product inside Postman's broader API platform.
Key Features
Fern's generated SDKs include real production-grade ergonomics beyond raw API wrappers, such as built-in authentication handling, automatic retries, pagination helpers, and support for streaming over Server-Sent Events or WebSockets, across languages including TypeScript, Python, Java, Go, Ruby, PHP, C#, Swift, and Rust.
The accompanying documentation sites include an always-in-sync API reference, versioning, search, an AI chat assistant, llms.txt and Model Context Protocol support for AI coding tools, and custom domain hosting, all generated from the same source specification used to build the SDKs.
Pricing
Fern's last publicly listed pricing, prior to its 2026 acquisition by Postman, offered three tiers: a free Hobby tier for small projects, a Team tier at one hundred fifty dollars per month for growing teams, and a custom-quoted Enterprise tier with SSO, RBAC, and self-hosted generation for larger organizations.
Pricing is structured around flat monthly fees tied to team members and AI credits rather than metered by API call or SDK download volume, though pricing details may evolve now that Fern operates within Postman.
Key Features
Multi-language SDK generation — Generates type-safe client SDKs in languages including TypeScript, Python, Java, Go, Ruby, PHP, C#, Swift, and Rust from a single API specification.
Automatic API documentation sites — Builds a full documentation website with an always-current API reference, versioning, and search directly from the same specification used for SDK generation.
Built-in retries and pagination — Generated SDKs include production-ready features like automatic retry logic and pagination helpers so developers do not have to hand-roll them.
Streaming support — SDKs and documentation support streaming responses over Server-Sent Events and WebSockets for real-time or long-running API interactions.
AI chat and MCP support — Documentation sites include an AI chat assistant and support llms.txt and Model Context Protocol integration so AI coding tools can consume API docs directly.
CLI-driven workflow — The fern CLI, with commands like fern init, fern check, and fern generate, integrates into CI pipelines to regenerate SDKs and docs whenever the API spec changes.
Broad spec format support — Accepts OpenAPI, AsyncAPI, GraphQL, Protobuf and gRPC, and OpenRPC specifications as input, rather than being locked to a single API description format.
Enterprise self-hosting — Enterprise customers can run the SDK and documentation generation pipeline within their own infrastructure for security and compliance requirements.
Pros & Cons
Pros
Single source of truth keeps SDKs and documentation permanently synchronized as the API evolves
Generated SDKs include real ergonomics like retries, pagination, and streaming rather than bare API wrappers
Supports a wide range of input specification formats beyond just OpenAPI
Backed by Postman's resources following the January 2026 acquisition, adding stability and integration potential
Cons
Post-acquisition roadmap and pricing under Postman are not yet fully settled or independently documented
Team tier at $150 per month may be a meaningful cost for very small startups compared to some free-tier competitors
Best suited to companies that already have or are willing to build a clean OpenAPI or equivalent specification
Smaller ecosystem and community track record compared to long-established API documentation tools
Pricing
Hobby Free Monthly
Team $150/month Monthly
Enterprise Custom pricing Custom
Frequently Asked Questions
What does Fern do?
Fern takes an OpenAPI, AsyncAPI, GraphQL, Protobuf, or OpenRPC specification and generates type-safe client SDKs in multiple programming languages along with a matching API documentation website from that same specification.
Is Fern free to use?
Fern offers a free Hobby tier for small projects with limited team members and AI credits, alongside paid Team and custom-priced Enterprise tiers for larger teams and organizations.
Which languages can Fern generate SDKs for?
Fern's generators cover languages including TypeScript, Python, Java, Go, Ruby, PHP, C#, Swift, and Rust, generated from a single underlying API specification.
Was Fern acquired?
Yes, Fern was acquired by Postman in January 2026, with the full Fern team joining Postman while Fern continues to operate as an independent product.
How is Fern different from Mintlify or ReadMe?
Fern differentiates itself by generating both SDKs and documentation from one specification, with documentation code snippets sourced directly from the real generated SDK code, while Mintlify and ReadMe have historically focused more narrowly on documentation hosting.
Can Fern be self-hosted?
Enterprise customers can run Fern's SDK and documentation generation pipeline within their own infrastructure as part of the Enterprise tier.