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Fern SDK Generator

Fern generates typed client SDKs from API specifications, adds tests and custom code, and publishes packages for multiple programming languages.

Fern SDK Generator

Fern turns OpenAPI, AsyncAPI, OpenRPC, gRPC, or Fern Definition files into client libraries for TypeScript, Python, Go, Java, Ruby, C#, PHP, Swift, and Rust. It can generate SDK code in the cloud or locally, add package metadata, run tests, and publish packages to registries such as npm, PyPI, and Maven.

Teams use it to maintain SDKs alongside evolving APIs. The generated libraries include typed models, pagination, retries, authentication helpers, webhook verification, documentation, and code samples. The pricing page lists Free and Enterprise plans; enterprise features include self-hosting, advanced access controls, and dedicated support.

Features

  • Generate SDKs from OpenAPI, AsyncAPI, OpenRPC, gRPC, or Fern Definition files
  • Support TypeScript, Python, Go, Java, Ruby, C#, PHP, Swift, and Rust
  • Generate strongly typed models, methods, documentation, and code snippets
  • Add custom code that survives SDK regeneration
  • Generate pagination, retries, idempotency, multipart uploads, SSE, and WebSocket support
  • Generate unit, mock-server, wire, and integration tests
  • Publish packages to registries including npm, PyPI, and Maven
  • Run generation in Fern Cloud or on your own infrastructure

Use cases

  • Generate client libraries for a public API
  • Publish SDK updates when an API specification changes
  • Create consistent SDKs across several programming languages
  • Add custom helpers without losing them during regeneration
  • Test generated clients against mock servers and live APIs
  • Publish versioned packages to language-specific registries

Pros

    Cons

      Latest updates

      • 3.106.1 (3.106.1)

        The generated API error’s requestId getter now works without configuration for APIs that return the request ID under a vendor-specific header.

      • 3.106.0 (3.106.0)

        The generated API error class’s requestId getter now reads the canonical X-Request-Id header.

      • 3.105.2 (3.105.2)

        The generated WebhooksHelper now consumes algorithm-header from api.settings.webhook-signature.

      • 3.105.1 (3.105.1)

        reference.md is now generated for every output mode.

      • 3.105.0 (3.105.0)

        Support inferred bearer auth with type: refresh-token; the SDK always sends grant_type: "refresh_token" to the get-token endpoint.

      Capabilities

      • Command line — “CLI Interact with your API from the terminal.” source
      • Self-hosted — “Run on our managed cloud, or self-host to meet stricter security, networking, and compliance requirements.” source
      • Official SDKs — “Fern generates and publishes client libraries, so you can focus on building the API.” source

      Get it

      Security

      • SOC 2 Type II — “SOC 2 Type II Report” source
      • SOC 2 — “SOC 2 Type II Report” source
      • GDPR — “SOC 2 Type II GDPR CCPA” source

      Pricing

      Starting price
      Free
      Prices checked
      2026-11-06

      Free

      Free

      • 10 team members
      • 1,000 pages
      • 250 AI credits per month
      • 2,000 page generations per month
      • Custom domain and subpath
      • Guides, API references, and changelogs

      Enterprise

      Price on request

      • SSO, SCIM, and advanced RBAC
      • Multiple repos and docs instances
      • Custom CSS, JavaScript, and React components
      • Custom layouts and design-system integration
      • Advanced analytics and data exports
      • Dedicated infrastructure, with self-hosting available
      Official website