MX
mxschmitt/zod-vs-ajv
Zod vs Ajv — Request Payload Validation
Comparison of Zod and Ajv for validating typed request payloads in TypeScript.
Run
npm install
npx tsx validate-zod.ts
npx tsx validate-ajv.tsKey Finding
Zod is the clear winner for TypeScript projects.
The decisive difference: with Zod, you define the schema once and derive the TypeScript type from it. With Ajv, you must define the TypeScript interface and the JSON Schema separately — maintaining two parallel definitions of the same shape.
// Zod: single source of truth
const Schema = z.object({ name: z.string(), age: z.number() });
type MyType = z.infer<typeof Schema>; // derived automatically
// Ajv: two definitions that must stay in sync
interface MyType { name: string; age: number }
const schema: JSONSchemaType<MyType> = { /* ...rewrite the same shape as JSON Schema... */ };Ajv's JSONSchemaType<T> catches mismatches at compile time, so the two definitions can't silently drift apart. But the duplication itself is the problem — it's more code, more maintenance, and more room for friction during refactors.
Comparison
| Zod | Ajv | |
|---|---|---|
| Schema = Type | Yes — z.infer derives the type |
No — interface and schema defined separately |
| Verbosity | Compact, chainable API | ~2x more code for the same shape |
| Transforms | Built-in (e.g. Set to Array) |
Not supported |
| Standard | Zod-specific | JSON Schema (language-agnostic) |
| Cross-language | No | Yes — JSON Schema works in any language |
When Ajv still makes sense
- You need to share schemas across languages (e.g. Python, Go, Java all validate the same payload)
- You're working with OpenAPI / Swagger, which uses JSON Schema natively
- You receive schemas at runtime from an external source
For everything else in TypeScript, use Zod.