Scalar JSON Schema Validator

Validate documents against a JSON Schema with Ajv and get short, human-friendly error messages.

This is the shared validation engine behind @scalar/openapi-validator. It knows nothing about OpenAPI or AsyncAPI, so you can use it with any JSON Schema.

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Installation

npm add @scalar/json-schema-validator

Usage

Pass a document (an object, or a JSON/YAML string) and a JSON Schema:

import { validate } from '@scalar/json-schema-validator'

const schema = {
  $schema: 'https://json-schema.org/draft/2020-12/schema',
  type: 'object',
  required: ['name'],
  properties: { name: { type: 'string' } },
}

const result = validate({ name: 'Hello' }, schema)

console.log(result.valid)

if (!result.valid) {
  console.log(result.errors)
}

The dialect is picked automatically from the schema's $schema (JSON Schema draft-04, draft-07, and 2020-12 are supported).

Reuse a schema

When validating many documents against the same schema, compile it once:

import { createValidator } from '@scalar/json-schema-validator'

const validateUser = createValidator(schema)

validateUser({ name: 'Ada' })
validateUser({ name: 'Grace' })

Extra formats

Register custom Ajv formats via formats:

validate(document, schema, {
  formats: {
    'media-range': true,
  },
})

Formats are applied when a schema is compiled, and validate caches the compiled schema by identity. So formats only takes effect the first time it sees a given schema object — later calls reuse the validator built from that first set. When different documents need different formats for the same schema, build a validator per format set with createValidator instead.

Throw on error

try {
  validate(document, schema, { throwOnError: true })
} catch (error) {
  // Handle the first validation error
}

Community

We are API nerds. You too? Let's chat on Discord: https://discord.gg/scalar

License

The source code in this repository is licensed under MIT.