effect-json-schema

Tiny Effect Schema adapter for Standard JSON Schema V1.

effect-json-schema keeps the runtime surface deliberately small: pass an Effect Schema, receive a Standard JSON Schema object with ~standard.version, ~standard.vendor, ~standard.types, and ~standard.jsonSchema.input/output.

Install

npm install effect-json-schema effect @standard-schema/spec

Usage

import * as S from "effect/Schema"
import { toStandardJsonSchema, type InferInput, type InferOutput } from "effect-json-schema"

const Person = S.Struct({ name: S.String })
const standard = toStandardJsonSchema(Person)

const jsonSchema = standard["~standard"].jsonSchema.input({
  target: "draft-2020-12"
})

type PersonInput = InferInput<typeof standard>
type PersonOutput = InferOutput<typeof standard>

Supported targets

The adapter supports every Standard JSON Schema V1 target required by the protocol:

• draft-2020-12
• draft-07
• openapi-3.0

Unknown target strings throw TypeError so future targets cannot silently produce incorrect schemas.

Input and output schemas

Effect transforms can have different encoded input and decoded output types. The adapter preserves that distinction by using Schema.encodedSchema for jsonSchema.input() and Schema.typeSchema for jsonSchema.output().

const TextToNumber = S.transform(S.String, S.Number, {
  strict: true,
  decode: (value) => Number(value),
  encode: (value) => String(value)
})

const standard = toStandardJsonSchema(TextToNumber)
standard["~standard"].jsonSchema.input({ target: "draft-07" })  // { type: "string" }
standard["~standard"].jsonSchema.output({ target: "draft-07" }) // { type: "number" }

libraryOptions

libraryOptions are forwarded to Effect's JSON Schema generator. For example, this enables Effect's additionalPropertiesStrategy option:

standard["~standard"].jsonSchema.input({
  target: "draft-07",
  libraryOptions: { additionalPropertiesStrategy: "allow" }
})

Quality gates

This repository is intentionally small, but CI is not minimal. Every push and pull request runs:

• TypeScript strict type-checking
• Build and declaration emit
• Vitest contract tests for the Standard JSON Schema protocol
• LOC, construct length, nesting, and marker-text gates
• Repository health checks for license, docs, templates, and workflows
• npm pack consumer smoke tests for runtime and type imports
• publint package checks

Run the full gate locally:

npm run ci

License

Apache-2.0. See LICENSE.