Fern vs Speakeasy
Fern has Swift and Rust SDKs so mobile teams stop hand-rolling, zero-dependency TypeScript so bundles stay lean, and docs that regenerate so code never drifts.
30-minute call. Side-by-side walkthrough on your spec.
Built for the long haul
Picking an SDK platform is a multi-year bet. Fern is backed by Postman with an extensive roadmap across SDKs, Docs, and the CLI, and every generator is open source so the pipeline is yours forever.
Generators are fully open source
Every generator is Apache-2.0 licensed on GitHub, so the pipeline is yours forever. You pay Fern for the hosted CI, registry publishing, and dedicated SDK engineers behind it.
Postman backing
Fern is backed by Postman, a company built entirely around API tooling. SDKs sit at the center of that roadmap, so we're here for the long haul.
SDKs are the core roadmap
Rust SDKs just shipped and a native CLI generator is on deck, with deeper protocol support and better ergonomics landing every quarter.
Why teams choose Fern over Speakeasy
9 languages, including Swift and Rust
TypeScript, Python, Go, Java, C#, PHP, Ruby, Swift, and Rust. Fern is the only platform with production-ready Swift. Speakeasy ships neither.
REST, WebSockets, and gRPC
OpenAPI, AsyncAPI, OpenRPC, gRPC, and the native Fern Definition. Speakeasy is OpenAPI-only.
Docs and SDKs from one source of truth
Reference docs, code samples, and SDKs regenerate together so nothing drifts. Includes Ask Fern, llms.txt, and an MCP server.
On-premise and SOC 2 Type II
Self-hosted deployment for regulated industries. SOC 2 Type II, 99.9% uptime SLA, audit trails for enterprise governance.
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 FellmanHead of Engineering, Developer Platform, Square
Side-by-side TypeScript comparison
Compare the generated code, not the dashboard. Below: Fern's Square SDK against Speakeasy's Cloudinary SDK, category by category.
| Category | Fern TypeScriptSquare SDK | Speakeasy TypeScriptCloudinary SDK |
|---|---|---|
| Dependencies | Zero-dependency TypeScript interfaces with tree-shakable serde. | Requires Zod as a peer dependency. Every model ships dual Zod schemas, adding ~13kB min+gzip before any SDK code. |
| Model output | Clean TypeScript types with no runtime scaffolding bolted on. | Models include schema machinery, $inboundSchema, $outboundSchema, $Outbound types, and standalone toJSON/fromJSON functions. |
| Response unions | Discriminated unions so consumers branch safely on response type. | Bare unions like SuccessResponse | AsyncAcceptedResponse with no discriminator. Consumers inspect properties manually. |
| Enum handling | Forward-compatible enums with unknown-value handling. New server values don't crash consumers. | Uses ClosedEnum for status and category enums. New server-side values can throw at runtime via Zod. |
| Test coverage | 146 auto-generated tests, including wire tests against a mock server. | No .test.ts, .spec.ts, or __tests__ files in the generated repo. |
| Boilerplate | Lean generated output. No deprecated scaffolding shipped on day one. | Heavy generated scaffolding. Example: source.ts takes 171 lines for two 3-line types. |
| Required params | Required params are validated at client initialization. | cloudName silently defaults to literal "CLOUD_NAME", producing valid-looking but broken URLs. |
| Retries | On by default: 2 retries with exponential backoff, jitter, and Retry-After support. | Defaults to strategy: "none", so users get no retry resilience unless they opt in. |
| Pagination | First-class pagination. Page<T> implements AsyncIterable for for await. | Cursor handling is manual. |
| Errors | Typed structured errors. Example: SquareError.errors includes typed category and code enums. | Returns raw body: string and leaks naming like data$ into the public API. |
| JSDoc examples | @example JSDoc on every method with runnable IDE snippets. | No @example tags. |
| Raw response access | .withRawResponse() is opt-in and returns an HttpResponsePromise that extends native Promise. | Result-style patterns and $inspect() concepts. |
| Naming consistency | Consistent generated naming conventions across resources. | Inconsistent AI vs Ai casing. data$ names bleed into the public API. |
| Auth plumbing | Auth surface is generated to match the spec. | Ships unused OAuth2 password-flow and OIDC scaffolding even for Basic-Auth-only APIs. |
| Additional features | Tree-shakeable subpackage exports, native BigInt serde, 8-runtime detection, webhook signature verification, structured pluggable logging. | Not highlighted. |
Square SDKFern is your SDK team
A Fern engineer pairs with you from spec review through first publish, then stays on as ongoing support.
- 1
Spec review and SDK design
Bring your OpenAPI, AsyncAPI, or gRPC spec. A Fern engineer reviews the surface and pairs with you on naming, errors, pagination, and audience tags.
- 2
First SDK in days, not quarters
Generated SDKs in your chosen languages on day one, with @example JSDoc, typed errors, and wire tests against a mock server.
- 3
Fern Replay: custom code preserved
Hand-written patches replay on every regen, tracked in .fern/ and visible in PR review. No more rebasing custom code each release.
- 4
Publish to every registry
npm, PyPI, Maven, NuGet, Packagist, RubyGems, Crates.io, and Swift Package Index. Versioning, changelogs, and release notes handled.
Common questions from teams evaluating Fern and Speakeasy
Want the full feature-by-feature comparison? Read the Fern vs Speakeasy blog post.
Get a side-by-side walkthrough on your spec
A Fern engineer walks you through your spec, your SDK surface, and how Fern compares to Speakeasy on the categories that matter to your team. No sales pitch, no slide deck.
Book a demo