Schema Libraries

Runtime parsing follows Standard Schema-style contracts where possible. OpenAPI conversion still depends on schema-library-specific adapters.

Zod v4

Zod schemas are converted through @asteasolutions/zod-to-openapi. Zod v4 is the target; Zod v3 is intentionally outside the compatibility surface.

Valibot

Valibot schemas are converted through @valibot/to-json-schema. Request schemas use input mode, while response schemas use output mode.

Effect Schema

Effect Schema can be passed directly to endpoint definitions. Runtime parsing uses Effect's Standard Schema adapter, while OpenAPI conversion uses Effect's JSON Schema generator.

import { Schema } from 'effect'

defineEndpoint({
  params: Schema.Struct({
    id: Schema.NumberFromString,
  }),
  responses: {
    200: Schema.Struct({
      id: Schema.Number,
      name: Schema.String,
    }),
  },
})

Effect schemas with runtime requirements are outside the supported contract surface. Use schemas whose Context is never.

Transforms and OpenAPI direction

For Valibot, request-side OpenAPI schemas use input mode and response-side schemas use output mode so transforms are represented in the right direction. Effect JSON Schema generation follows Effect's own JSON Schema rules.

import * as v from 'valibot'

const Id = v.pipe(v.string(), v.transform(Number), v.number())

defineEndpoint({
  body: v.object({ id: Id }), // OpenAPI request schema: string
  responses: { 200: v.object({ id: Id }) }, // OpenAPI response schema: number
})

Response validation uses the validator output on the server. Generated clients then apply the JSON wire mapping used by the supported Nitro line. A response output containing Date, for example, is validated as Date but exposed to clients as string. Request inputs, server outputs, and client wire values are distinct boundaries.