API contract checks
Verify request and response payloads before integrating an API or shipping a client change.
JSON Schema tool
JSON Schema Validator Online
Paste JSON data and a JSON Schema to verify required fields, data types, nested objects, arrays, enums, patterns and common numeric or string constraints. Use it to debug API payloads, configuration files and test fixtures before they reach production.
How to validate JSON against a schema
Step 1
Paste the JSON document you want to validate into the JSON data field.
Step 2
Paste the JSON Schema that describes the expected structure and constraints.
Step 3
Select Validate against schema and review each error path before changing the payload or schema.
If the document cannot be parsed as JSON at all, fix the syntax first. Once parsing succeeds, schema validation answers the next question: does this otherwise valid JSON contain the fields, types and values the consuming system expects?
Example: valid JSON that fails its schema
The following payload is valid JSON syntax, but it violates the example schema in three different ways: id is a string instead of an integer, the required email property is missing, and extra is not permitted because additionalProperties is false.
Failing JSON
{
"id": "42",
"active": true,
"extra": "unexpected"
}Expected errors
$.id — expected integer, received string.
$.email — required property is missing.
$.extra — additional property is not allowed.
Common JSON Schema validation use cases
Configuration validation
Check application, deployment, feature-flag and service configuration files against the structure your system expects.
Test fixtures and mocks
Catch incorrect field types or missing required properties in mocked API responses and automated-test fixtures.
Data pipeline debugging
Separate malformed JSON syntax from structurally valid JSON that does not satisfy downstream contract requirements.
What this validator checks
This browser implementation covers common JSON Schema constraints used in everyday API and configuration validation: type, required, properties, items, enum, pattern, minLength, maxLength, minimum, maximum, and additionalProperties: false.
Validation is recursive for nested objects and array items. Error messages include a JSON-style path such as $.user.email or $.roles[0] so you can identify the property that failed rather than only receiving a generic pass or fail result.
JSON validation vs JSON Schema validation
A normal JSON validator checks whether the text follows JSON syntax. Schema validation starts after parsing succeeds and checks whether the resulting data has the structure and values your system expects. Valid JSON can still fail because an id is a string instead of an integer or because a required field is missing.
Limitations and edge cases
This tool is intentionally not presented as a full standards-complete validator for every JSON Schema draft. Advanced keywords such as composition rules, references, conditional schemas, custom formats and draft-specific behavior may require a standards-complete library in your application or CI pipeline. Use this page for common structural checks and fast debugging.
Continue the JSON Schema workflow
Frequently asked questions
What is a JSON Schema validator?
A JSON Schema validator compares parsed JSON data with a schema that defines expected types, required properties, nested structures and other constraints. Valid JSON syntax can still fail schema validation.
Does this tool validate every JSON Schema keyword?
No. This browser validator intentionally supports common everyday constraints such as type, required, properties, items, enum, pattern, string and numeric limits, and additionalProperties false. It is not a complete implementation of every JSON Schema draft or advanced keyword.
Is my JSON uploaded to FixTools?
No. Validation runs locally in your browser. The JSON document and schema do not need to be uploaded to FixTools for this tool to work.
Why can valid JSON fail JSON Schema validation?
JSON syntax only proves that the text can be parsed. Schema validation can still fail when a field has the wrong type, a required property is missing, a value does not match a pattern or enum, or an unexpected property is present.
What should I do if the JSON itself will not parse?
Fix the syntax first with the JSON validator or JSON error tools, then return to schema validation after the document parses successfully.