Validate JSON against a schema
Paste a JSON Schema on the left and your data on the right. Powered by Ajv — the fastest JSON Schema validator available. Supports draft-07, 2019-09, and 2020-12. Nothing leaves your browser.
Uses Ajv under the hood — the industry-standard JSON Schema validator, trusted by millions of Node.js projects.
Every failing field is reported with its JSON Pointer path and the exact schema rule that rejected it.
Draft-06, 07, 2019-09, and 2020-12 are all supported. Declare your draft with $schema.
Validates format keywords: email, uri, date, date-time, ipv4, ipv6, uuid, and more via ajv-formats.
All validation runs in your browser. Your schema and data are never sent to a server.
Validation reruns on every keystroke with a short debounce — no button to click.
Examples
Schema: { "type": "object", "properties": { "age": { "type": "integer" } } }
Data: { "age": "thirty-six" }/age · type must be integer
Schema: { "type": "object", "required": ["name", "email"] }
Data: { "name": "Ada" }(root) · required must have required property 'email'
Schema: { "properties": { "role": { "enum": ["admin","editor","viewer"] } } }
Data: { "role": "superuser" }/role · enum must be equal to one of the allowed values
Use cases
- API contract validation
Define your API's request/response shape as a JSON Schema and validate payloads before they hit your handler — catch malformed requests at the boundary.
- Config file linting
Write a schema for your application's config.json and validate it in CI. Catch missing required fields or wrong value types before they crash production.
- Form data validation
Share one JSON Schema between your backend (Ajv) and frontend (react-hook-form + @hookform/resolvers). Single source of truth for validation rules.
- Testing API responses
Assert that your API still returns the expected shape after refactors. Paste a response and validate it against your documented schema.
- Data pipeline guards
Validate incoming records in an ETL pipeline before writing to a database. Surface schema violations early rather than at query time.
From the JSON FYI guides
In-depth explanations for common JSON errors and patterns.
A complete syntax overview of JSON's six value types and grammar rules.
Strings, numbers, booleans, null, arrays, objects — with edge cases.
The mistakes that cause 90% of parse failures, with fixes.
Naming, nullability, dates, and error envelope conventions.
Frequently asked questions
What is JSON Schema?+
JSON Schema is a vocabulary for annotating and validating JSON documents. You write a schema — a JSON document that describes the allowed structure, types, required fields, and constraints — and then validate data against it. The current standard is draft 2020-12, though draft-07 is still widely used.
What JSON Schema drafts are supported?+
This validator uses Ajv, which supports JSON Schema draft-06, draft-07, draft-2019-09, and draft-2020-12. Declare your draft with the $schema keyword and Ajv automatically selects the right validation rules.
What do the error paths mean?+
Error paths use JSON Pointer notation (RFC 6901): a leading slash followed by property names and array indices, e.g. /users/0/email. A path of '(root)' means the top-level value itself failed validation.
Is my data uploaded anywhere?+
No. All validation runs in your browser using Ajv. Nothing is sent to a server.
What is 'additionalProperties: false'?+
It tells the schema validator to reject any property not listed under 'properties'. Useful for strict API contracts where unknown fields should be flagged.
Can I validate arrays of objects?+
Yes. Set the schema type to 'array' and use the 'items' keyword to define the schema each element must match.