Zod 4.3 introduced fromJSONSchema(). We
were using @cfworker/json-schema in Fragno Forms to validate form submissions on the
backend. Since we already use Zod for request schemas, switching to Zod for JSON Schema validation
would let us consolidate dependencies.
Why not use Ajv?
Ajv is the go-to JSON Schema validator, but it uses new Function() under
the hood to generate optimized validation code. Cloudflare Workers (the workerd runtime) doesn't
allow dynamic code evaluation, which is a problem since this website runs on Cloudflare Workers.
@cfworker/json-schema exists specifically for this constraint. It's a pure runtime interpreter
that works in restricted environments. But if you're already using Zod, having it handle JSON Schema
validation means one fewer dependency.
Benchmark
I ran a quick benchmark against the JSON-Schema-Test-Suite (draft7). In serverless environments, validators don't persist across requests, so caching compiled schemas isn't practical, we need to measure combined compile + validate time.
| Library | Version | Compile | Validate | Total |
|---|---|---|---|---|
@cfworker/json-schema | 4.1.1 | 0.0003ms | 0.0007ms | ~0.001ms |
zod | 4.3.5 | 0.011ms | 0.0006ms | ~0.012ms |
ajv | 8.17.1 | 2.0ms | 0.00009ms | ~2.0ms |
Ajv is slowest overall because code generation is expensive, but once compiled validation is
extremely fast. Zod is slower than @cfworker/json-schema but still fast enough for most use cases.
Dependencies
Additionally, @jsonforms/core has an Ajv dependency for frontend validation. Removing
@cfworker/json-schema means many users go from three validation libraries to two. Ideally we'd use
just one, but JSONForms doesn't allow swapping out its validation library.
We dropped @cfworker/json-schema from Fragno Forms. Zod was already there for validating
backend route inputs, and performance is more than acceptable for this use case.