All 188 Dependencies

Every package Fern depends on, ranked by repo health score.

Fern is an open-source developer-experience platform for API providers. Point it at an OpenAPI spec (or its own more expressive Fern Definition YAML, plus AsyncAPI and Protobuf support), and its CLI compiles that definition into a versioned Intermediate Representation that every downstream generator consumes. From that single IR, Fern produces idiomatic, type-safe client SDKs for TypeScript, Python, Java, Go, Ruby, PHP, C#, Rust, and Swift, plus server boilerplate and an OpenAPI spec exporter for teams that started from Fern's own definition format.

Beyond code generation, Fern builds and hosts a full documentation website from the same API definition: an interactive API reference, versioned markdown pages, dark mode, and an AI-powered search assistant trained on a team's docs, APIs, and SDKs. Docs built with Fern are used in production by companies like ElevenLabs, LaunchDarkly, and Hume — the CLI can scaffold and preview these sites locally before publishing.

The project originated from Y Combinator's 2023 batch and is maintained by Birch Solutions under the Fern name. It's structured as a large TypeScript monorepo (pnpm + Turborepo) containing the CLI, the IR compiler, the OpenAPI/AsyncAPI/Protobuf importers, every per-language generator, and a `seed/` directory of golden-file SDK fixtures used to regression-test all nine generators on every change. Language generators also ship as Docker images (the `fernapi/fern-*-sdk` family) so they can run locally or in Fern's remote generation service.

Fern's differentiator versus generating SDKs directly from OpenAPI templates is that IR-first design: adding a new spec format doesn't require touching nine generators, and the IR can evolve (via a dedicated `ir-migrations` package) without breaking SDKs already generated by older CLI versions. The CLI itself, all generators, and the OpenAPI/Protobuf importers are Apache-2.0 licensed and free to self-run; the hosted docs dashboard and AI search are Fern's commercial SaaS offering.

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All 188 Dependencies

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