Comparison
SDKs + docs generated from an API spec (OpenAPI or Fern Definition) — and how that lines up against a TypeScript-only, zero-touch generator that auto-rebuilds on every schema change.
Last reviewed: April 23, 2026
TL;DR
Fern sits in a slightly different category. It generates SDKs, yes, but the real pitch is the triple play: SDKs + API docs + server stubs from a single source of truth. That source can be OpenAPI, or it can be Fern Definition — a proprietary IDL Fern built to work around OpenAPI's rough edges.
SDK Factory is single-purpose by design. We generate and publish a TypeScript SDK from your OpenAPI schema. We don't produce a docs site, we don't scaffold server code, and we don't ask you to adopt a new IDL. If OpenAPI is already your source of truth and you want the SDK half handled well without buying into a bigger ecosystem, that's the shorter path.
The honest version: if you're starting from scratch and want a unified spec → SDK + docs story, Fern is more ambitious and probably worth learning. If you already have an OpenAPI document in production, adding a fern/ directory and migrating to Fern Definition is work you can skip.
Compiled from Fern’s public documentation at the time of the last review date above.
The concrete shape of the integration — a file that lives in your repo vs a URL pasted into a dashboard. Same outcome, very different footprint.
fern/
├── fern.config.json
├── generators.yml
└── api/
└── openapi.yml
# generators.yml
default-group: ts
groups:
ts:
generators:
- name: fernapi/fern-typescript-node-sdk
version: 0.13.0
output:
location: npm
package-name: "@acme/api-client"
token: ${NPM_TOKEN}Past the pitch — what actually happens on day one, when the schema drifts, and when the upstream breaks.
Fern
`npm install -g fern-api`, `fern init`, hand-edit fern.config.json and generators.yml, wire fern generate into CI, merge a PR that lands the fern/ directory in your repo, watch CI publish.
SDK Factory
Open the dashboard, paste the OpenAPI URL, pick a registry, click publish. First version is out in minutes. No repo changes, no CI wiring.
Fern
You edit the spec. CI runs fern generate on the next push and (if you wired it up) a bot commits the updated generated code and republishes. Behind a merge gate.
SDK Factory
We poll the schema URL, see the new hash, build and publish a patch. Nobody in your team needs to do anything.
Fern
Fern's strength: `fern generate --group docs` produces a hosted docs site tied to the same spec. Everything stays in sync because it's one source.
SDK Factory
Not our scope. Keep whatever docs pipeline you already run (Redocly, Swagger UI, Mintlify). Your OpenAPI can feed both SDK Factory and your docs independently.
Free Starter tier, paid Pro tier per generator, Enterprise pricing on request
Free (1 app). $10/mo Premium (5 apps). $30/mo Pro (unlimited apps + rollback). Published publicly, no sales call.
View our pricingFern can emit OpenAPI from its own IDL. If your source of truth is Fern Definition, run `fern write-openapi` (or the equivalent for your Fern version) and publish the OpenAPI file at a stable HTTPS URL. If OpenAPI is already your spec, skip this step.
SDK Factory doesn't generate docs. If Fern was also your docs host, pick a replacement before you cut over (Redocly, Mintlify, Swagger UI on your own hosting, or leave the existing Fern docs running alongside). Treating docs and SDK as separate concerns is cleaner in the long run.
Publish the new SDK under a distinct name (e.g. `@acme/api-client-v2`) so both SDKs coexist during the transition. Install it in a pilot consumer first.
Expect small per-consumer refactors: the Fern-generated TypeScript client and ours don't share call signatures. Keep both published until every consumer has migrated. There's no pressure to rush — SDKs can sit on a registry indefinitely.
Once every consumer is migrated, remove the fern/ directory, drop any CI steps that ran `fern generate`, and revoke the npm token Fern was using. If you kept Fern for docs, that side continues untouched.
No. SDK Factory consumes OpenAPI 3.x only. If your source of truth is Fern Definition, you'd need to export OpenAPI from Fern (it supports that) and point us at the exported URL — but at that point you're running two tools to do one job, which is probably not what you want.
No. We publish a TypeScript SDK — that's the scope. If you already have a docs pipeline (Redocly, Swagger UI, Stoplight, Mintlify…) it continues to work, and our SDK is one of many consumers of your OpenAPI schema.
Fern's TS SDK is one of seven similar-shape SDKs — a useful property if you staff SDK maintenance across multiple languages. Ours is TypeScript-first: ESM + CJS + bundled .d.ts, Zod-validated request and response, typed errors per operation, retries and timeouts built in. If you only ship TS, the depth is better with us.
Technically yes — they both consume OpenAPI independently. You'd end up publishing two TS SDKs to different package names (or different registries), which only makes sense during a migration. Long-term, pick one.
You can export the last-published tarball from S3 at any time and lift it into a hand-maintained package. We also publish via standard npm / GitHub Packages / custom registries, so swapping back to Fern or in-housing the pipeline is mostly a matter of changing which upstream produces the tarball.
One app on the Free tier, no card required. Decide whether it’s a better fit than Fern with your actual schema, not a benchmark.