Validate JSON Against a Schema
Paste a JSON document in one pane and a JSON Schema in the other, and the validator — powered by Ajv, the de-facto fastest JSON Schema engine — compiles the schema, runs the document against it, and produces the full list of validation errors in a single pass. Each error names the exact JSON Pointer path that failed and the specific keyword (type, required, enum, pattern, minLength) that rejected the value.
Use this to validate an API request or response against its documented contract, verify a configuration file matches a published schema (OpenAPI component, package.json, tsconfig.json, a custom internal schema), check that a test fixture is still valid after a schema update, sanity-check data incoming from a third party, or explore a schema interactively by iterating on the data until validation passes.
Full JSON Schema Draft-07 is supported including $ref, allOf/anyOf/oneOf/not, conditional if/then/else, pattern and format checks, and nested object constraints. All errors surface at once rather than stopping at the first failure, which saves round-trips when the data has several independent issues, and a sample schema with common patterns is available as a starting point when you are learning the specification.
Both the schema and the document stay in your browser — Ajv runs locally, which matters when either input contains proprietary structure or real customer data.
About JSON Schema validation
JSON Schema defines the structure, types, and constraints of JSON data. It's used for API request/response validation, configuration file validation, and data quality checks.
- Full JSON Schema Draft-07 support
- All validation errors shown at once
- Exact error paths and descriptions
- Real-time validation as you type
- Sample schema with common patterns
100% client-side. Your inputs never leave your browser. Ads via AdSense (consent required).
Frequently asked questions
How do I validate JSON against a JSON Schema?
Paste the schema on one side and the data on the other; the validator runs the data against the schema (draft-07 by default) and reports every violation with a JSON Pointer path, the failing keyword (type, required, minLength, pattern, etc.) and a human-readable reason. If the data is valid, you get a green check. Both inputs are live — editing either re-runs validation instantly.
Is the JSON Schema validator free?
Yes, fully free with no signup or usage cap. Validate unlimited documents against unlimited schemas — useful for API contract testing, OpenAPI spec validation, config linting and CI pipelines. JSONCraft has a single open tier; every tool including this one is fully available with no premium features behind a gate.
Does the validator upload my schema or data?
No. Validation runs entirely in your browser using a client-side JSON Schema implementation. Nothing is sent anywhere, which matters because schemas often describe internal data models (user records, payment payloads) and the sample data often is real production output. You can validate safely without any data or schema structure leaking.
Does it support $ref and remote schemas?
Local $ref to other definitions in the same schema works out of the box — use $ref: "#/definitions/Foo" style pointers. Remote $ref to external URLs is intentionally not fetched — that would require a network call and the tool is strictly client-side. If your schema uses external $ref, inline those definitions into a single combined schema before validating here.
Which draft of JSON Schema does it support?
Draft-07 is the default because it has the widest tool support and is what most OpenAPI 3.0 specs use. Later drafts (2019-09, 2020-12) introduced significant changes like $defs replacing definitions and unevaluatedProperties; if your schema uses those keywords explicitly, targeting draft-07 will be stricter about unknown keywords. For pure draft-07 data/schema pairs, the validator is 100% spec-compliant.
Sources (1)
- Wright, A., Andrews, H., Hutton, B., & Dennis, G. (2022). JSON Schema: A Media Type for Describing JSON Documents. Internet-Draft draft-bhutton-json-schema-01, IETF (2020-12 dialect, json-schema.org).
These are the specifications and standards this tool implements.
Related guides
- JSON Schema Essentials — Validation, Types, and Common PatternsA practical guide to JSON Schema Draft 7, 2019-09 and 2020-12: types, keywords, $ref, conditional validation, and the patterns that ship in production APIs.
- JSON Security Pitfalls — Prototype Pollution, DoS, and Parsing AttacksEvery JSON input is attacker-controlled until proven otherwise. Prototype pollution, parser DoS, deep nesting — the attacks that actually ship against JSON endpoints.
By Marco B. ·