JSON Schema Validator

How to use the JSON Schema Validator

Validate any JSON payload — an API response, webhook body, fixture, config file, or OpenAPI component example — against a JSON Schema (Draft-07, 2019-09, or 2020-12). Powered by Ajv in the browser, the validator reports precise JSON Pointer error paths, supports $ref resolution, and can infer a starter schema from a sample with the companion Schema Inspector. Use it to test API contracts, confirm fixtures, and harden CI validation.

What it does

• Validates JSON against a schema with full Ajv coverage of keywords (type, required, enum, pattern, format, oneOf, allOf, anyOf, $ref).
• Reports each error with a JSON Pointer path, keyword, and human-readable message.
• Infers a schema from a sample payload as a starting draft via the Schema Inspector.
• Supports Draft-07, 2019-09, and 2020-12; auto-detects via $schema.
• Validates arrays of records, nested objects, and discriminated unions (oneOf with const).
• Shows schema lint, coverage, and generated negative cases to harden your contract.

When to use it

• Confirm an API response matches the documented contract before testing further.
• Validate webhook payloads from third parties (Stripe, GitHub, Slack, etc.).
• Test an OpenAPI component schema against real sample data.
• Build contract tests for QA without writing code.
• Lock down configuration files in your CI pipeline.
• Author a new schema by inferring from a representative sample, then tightening it.

How to use it

1. Paste your JSON payload on the left and the JSON Schema on the right.
2. Pick the schema draft (or leave it on auto-detect via $schema).
3. Validation runs automatically — passing payloads show a success indicator; failures list each error with the JSON Pointer path.
4. Don't have a schema yet? Use the Schema Inspector to generate a starter draft from your sample, then edit and tighten.
5. Copy the report to a ticket, or copy the schema once you're satisfied.
6. Send the validated payload to JSONPath Tester for query checks, or use the Schema Inspector to explore structure.

Tips & pitfalls

• Add "additionalProperties": false to fail on unexpected fields — most contract bugs sneak in this way.
• A field listed in properties is not required by default — add it to the required array explicitly.
• Use format: "date-time", "email", "uuid" for string validation; enable format checking explicitly.
• Draft-07 uses definitions; 2019-09+ uses $defs. Match the draft your toolchain expects.
• For nullable fields, use "type": ["string", "null"] — there is no nullable: true in standard JSON Schema (that's OpenAPI 3.0 sugar).
• For OpenAPI 3.0 schemas, convert nullable: true and the example keyword as needed.

FAQ

• How do I validate JSON against a schema online? Paste the JSON and the schema into the two editors. Errors appear instantly with the path and reason.
• Which JSON Schema drafts are supported? Draft-07, 2019-09, and 2020-12. The tool auto-detects from $schema or you can pick manually.
• How do I generate a JSON Schema from a sample? Use the Schema Inspector on a representative JSON payload — it produces a starting draft you can tighten.
• Why is my "required" field not failing? The required array must be declared at the object level whose keys it constrains. Putting it inside a property definition has no effect.
• Is my JSON or schema uploaded? No. Validation uses Ajv in your browser. Nothing is sent to a server or logged.
• Can it validate OpenAPI component schemas? Yes — paste the component schema and a sample payload, and pick an OpenAPI mode. OpenAPI 3.0 nullable: true is handled for you.

Related tools

• Validate an agent tool contract in the Agent Debugging & Integration Toolkit.
• Format and validate JSON before checking it against a schema.
• Diff two JSON documents to see what changed between payloads.
• Generate and apply JSON Patch using the JSON Pointer paths in your errors.
• Test JSONPath expressions against a validated payload.
• Convert cURL commands to capture the API response you want to validate.

Use-case guides

• Validate OpenAPI schema example JSON

Runs locally in your browser. Powered by Ajv. No uploads. No analytics on pasted JSON.