JSON Schema Validator Online

Validate JSON against a JSON Schema with detailed error messages

Paste a JSON Schema and JSON data to validate

Or load one of the examples above to see it in action

About this tool

JSON Schema Validator Online is a free browser-based tool that validates any JSON document against a JSON Schema and shows detailed, human-readable error messages. It uses AJV (Another JSON Validator) — the fastest and most widely used JSON Schema validator — with full support for Draft-07 and common string formats like email, uuid, date-time, and uri.

Paste your JSON Schema on the left and your JSON data on the right. Results update automatically. Each validation error shows the exact path in your JSON that failed, the validation keyword that triggered the error, and a clear explanation of what went wrong — making it easy to debug schema issues in API payloads, AI structured outputs, configuration files, and form data.

All validation runs locally in your browser using AJV compiled to WebAssembly-friendly JavaScript. Your data is never sent to any server.

Common use cases

  • Validate OpenAI structured output responses against your function calling schema.
  • Test JSON Schema definitions before using them in your codebase.
  • Debug API request/response payloads that fail schema validation.
  • Validate configuration files against a defined schema.
  • Test AJV-compatible schemas for use with Express, Fastify, or NestJS validators.
  • Verify form submissions match expected data shapes.
  • Check that database seed data matches your schema before importing.
  • Validate LangChain or CrewAI tool output schemas.
  • Catch schema errors (wrong types, missing required fields, extra properties) quickly.
  • Use alongside the JSON Schema Generator to test generated schemas.

Frequently Asked Questions

What JSON Schema versions are supported?

This tool uses AJV which fully supports Draft-07 (the most widely used version, required by OpenAI function calling). It also handles most Draft 2019-09 and Draft 2020-12 keywords via AJV's compatibility layer.

What string formats are supported?

AJV with ajv-formats supports: date, date-time, time, duration, email, idn-email, hostname, idn-hostname, ipv4, ipv6, uri, uri-reference, iri, iri-reference, uri-template, json-pointer, relative-json-pointer, regex, and uuid.

What does "allErrors" mode mean?

By default, some validators stop at the first error. This tool uses allErrors: true so every validation error in your JSON is reported at once — not just the first one. This makes debugging much faster.

What does the error path mean?

The error path shows exactly where in your JSON the validation failed. For example, /user/email means the email field inside the user object failed. (root) means the top-level value itself failed.

Is my data sent to a server?

No. AJV runs entirely in your browser via JavaScript. Nothing is uploaded or stored.

Can I use this with OpenAI function calling schemas?

Yes. OpenAI function calling schemas are Draft-07 JSON Schemas. Paste the schema from your tool definition and validate sample AI outputs against it.

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