CornerTools

JSON Schema Validator

Validate JSON data against JSON Schema with clear errors and draft support.

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Validation result

Enter JSON schema and instance to validate

Checks JSON data against a JSON Schema and lists every rule it breaks, with the path to the failing value. It supports drafts 06, 07, 2019-09 and 2020-12, and runs in your browser.

How to use it

Paste the schema into JSON Schema and the data into JSON instance. The result updates as you type: a confirmation with the draft used, or a table of errors with the path, the rule and a message; the lines at fault are highlighted in the data. A syntax error shows under its field, with its line and column, and must be fixed first.

  • Schema draft — Auto-detect reads the $schema URL and falls back to draft 07. A schema that names draft 04 or 03 is reported as unsupported.
  • Fail on additional properties — off by default, as the JSON Schema standard allows extra keys. On, any schema that lists properties without saying otherwise rejects keys it does not list, as if it declared "additionalProperties": false. Each schema under allOf then rejects the keys the others list, so data combining them fails.
  • Strict tuple validation — reports tuple schemas that do not fix the array's length.

How validation works

Validation uses Ajv, a widely used JSON Schema validator, and reports all errors rather than stopping at the first. Formats such as email, date, date-time, uri and uuid are checked.

Unknown keywords and ambiguous schemas are listed as warnings below the result, and validation still runs: typos like requried show up rather than silently doing nothing, while annotations such as example or OpenAPI's nullable do not block the check.

Examples

Four rules broken at once

Schema
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "required": [
    "name",
    "email"
  ],
  "properties": {
    "name": {
      "type": "string",
      "minLength": 1
    },
    "email": {
      "type": "string",
      "format": "email"
    },
    "age": {
      "type": "integer",
      "minimum": 0
    }
  },
  "additionalProperties": false
}
Data
{"name":"","email":"anna@","age":-3,"role":"admin"}
Errors
 (additionalProperties): must NOT have additional properties
/name (minLength): must NOT have fewer than 1 characters
/email (format): must match format "email"
/age (minimum): must be >= 0

See also