JSON Schema validator

About this tool

This tool supports a bounded subset of the selected JSON Schema dialect; unsupported features are explicitly rejected. Check a JSON document against a schema using an explicitly selected Draft 7, 2019-09 or 2020-12 engine. A disposable browser worker parses, compiles and validates both inputs locally, with a two-second deadline that includes startup. Results distinguish invalid data from an unusable schema, unsupported features and an incomplete run. Diagnostic reports include document paths, schema paths and keyword names; they exclude raw values and exception messages, but property names can still reveal sensitive information.

Executable schema and document examples

{
  "draft": "draft7",
  "schema": {
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "age": {
        "type": "integer",
        "minimum": 0
      }
    },
    "required": [
      "name"
    ],
    "additionalProperties": false
  },
  "instance": {
    "name": "Avery",
    "age": 28
  }
}

{
  "status": "valid",
  "keywords": []
}

{
  "draft": "draft7",
  "schema": {
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "age": {
        "type": "integer",
        "minimum": 0
      }
    },
    "required": [
      "name"
    ],
    "additionalProperties": false
  },
  "instance": {
    "age": 28
  }
}

{
  "status": "invalid",
  "keywords": [
    "required"
  ]
}

{
  "draft": "draft7",
  "schema": {
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "age": {
        "type": "integer",
        "minimum": 0
      }
    },
    "required": [
      "name"
    ],
    "additionalProperties": false
  },
  "instance": {
    "name": "Avery",
    "age": "28"
  }
}

{
  "status": "invalid",
  "keywords": [
    "type"
  ]
}

{
  "draft": "2019-09",
  "schema": {
    "type": "array",
    "items": {
      "type": "integer"
    },
    "minItems": 2,
    "uniqueItems": true
  },
  "instance": [
    1,
    1
  ]
}

{
  "status": "invalid",
  "keywords": [
    "uniqueItems"
  ]
}

{
  "draft": "2020-12",
  "schema": {
    "$defs": {
      "positive": {
        "type": "integer",
        "minimum": 1
      }
    },
    "type": "object",
    "properties": {
      "count": {
        "$ref": "#/$defs/positive"
      }
    },
    "required": [
      "count"
    ]
  },
  "instance": {
    "count": 3
  }
}

{
  "status": "valid",
  "keywords": []
}

{
  "draft": "draft7",
  "schema": {
    "$ref": "#/definitions/value",
    "definitions": {
      "value": {
        "type": "string"
      }
    },
    "minLength": 3
  },
  "instance": "ok"
}

{
  "status": "valid",
  "keywords": []
}

{
  "draft": "2020-12",
  "schema": {
    "$ref": "#/definitions/value",
    "definitions": {
      "value": {
        "type": "string"
      }
    },
    "minLength": 3
  },
  "instance": "ok"
}

{
  "status": "invalid",
  "keywords": [
    "minLength"
  ]
}

Common validation mistakes

• Selecting 2020-12 for a schema that declares Draft 7, or assuming the tool auto-detects the dialect.
• Expecting properties alone to require a property: use required to require its presence.
• Expecting the string "28" to satisfy type: integer; the tool never coerces input types.
• Using an external $ref URL or an unknown extension keyword and assuming it was checked.
• Treating a format annotation as a format assertion, or a timeout as a valid result.
• Sharing a paths-only report without checking the property names it exposes.

Limits and notes

• —The supported dialects are Draft 7, 2019-09 and 2020-12. $schema declarations must match the selected dialect. Only fragment references beginning with # are accepted, and they must resolve inside the supplied schema. External schemas are never fetched. Unknown/custom keywords, custom dialects, $vocabulary, $async and OpenAPI nullable are unsupported. A __proto__ entry in a schema map is also rejected because of an engine limitation; document keys remain ordinary input data. Nested $id resources are unsupported; a root $id is allowed. unevaluatedItems and unevaluatedProperties are explicitly unsupported because this local engine does not handle all of its interactions reliably. $dynamicRef, $dynamicAnchor, $recursiveRef and $recursiveAnchor are also unsupported; ordinary local $ref recursion is supported. Percent-encoded slashes (%2F) in reference fragments are unsupported because of engine ambiguity. Use the JSON Pointer escape ~1 for a slash inside a property name. Arrays in dependencies or dependentRequired cannot contain an empty-string property name; required arrays can.
• —format is annotation-only in this tool: format: "email" does not reject an invalid email string. No type coercion, default insertion or additional-property removal is performed. A passing result covers the selected dialect and these local checks, not application business rules or a different validator’s configuration.
• —Each input is capped at 200,000 UTF-8 bytes, depth 64 and 20,000 JSON values. Regular-expression patterns are capped at 512 characters. Compilation and validation run in a disposable worker with a 2,000 ms deadline including worker startup. Large schemas, recursive references or expensive regular expressions may stop at a limit or time out; no passing result is inferred. The two-second deadline is a browser timer: background-tab scheduling can delay termination. A worker isolates UI execution, not memory usage. Additional complexity limits allow at most 512 schema objects and 512 entries in each direct schema-child list. The conservative estimated-work budget is document JSON value count multiplied by schema object count, capped at 200,000. Errors are nonexhaustive: the validator reports the first failure per evaluated branch, so correcting one error may reveal another. Each run is additionally capped at 50,000 weighted validation work units. Charges account for direct schema-child count and current document collection width, bounding repeated or exponential reference work.
• —Duplicate decoded object keys, unsafe integers, non-finite numeric overflow and nonzero underflow to zero are rejected before validation. Other decimals use JavaScript IEEE-754 numbers and can be rounded; this tool does not implement arbitrary-precision JSON arithmetic. Represent exact large identifiers as strings with a matching schema.
• —At most 100 diagnostics are returned, with each path limited to 2,048 characters. A truncation notice means details were omitted. The report contains paths and keyword names rather than raw input values, validator parameters or raw parser errors. Paths may contain identifying property names; reports are not anonymized. Inputs are processed in the loaded page and are not uploaded or persistently stored. Cancelling, replacing a run, changing inputs or leaving the tool terminates its worker. Clipboard copies and downloaded files are outside the page’s control. This is a bounded local implementation, not a claim of unrestricted JSON Schema conformance.

Frequently asked questions

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