Field-based JSON generation
Define names and types such as email, UUID, date, integer, enum, boolean, object, or array.
Runs in your browser · Data is not saved
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Free OpenAPI developer tool
JSON test data generator
Generate realistic mock API payloads from field definitions or OpenAPI schemas in JSON and YAML.
Describe your payload
Choose the input that matches what you already have.
Format: fieldName: type. Try email, uuid, date, datetime, integer(1, 100), enum(a, b), boolean, object, or array<string>.
Generated payload
JSON preview
Choose your fields or schema, then select Generate JSON. Results will appear here.
Generates sample fixtures, not a validation certificate. Complex schema rules need an explicit example. See supported features and test cases.
Private by design: generation happens locally in your browser. Field definitions, OpenAPI schemas, and generated payloads are not uploaded or stored.
JSON mock data generator
Create realistic test payloads from fields or OpenAPI
Generate one or many JSON records for API development and testing. Start with simple field definitions, or paste an OpenAPI 3 schema in JSON or YAML and select a component schema.
OpenAPI schema support
Generate data from properties, formats, enums, examples, arrays, objects, and local schema references.
Browser-only processing
Your field definitions, OpenAPI specification, and generated records are not uploaded or stored.
Useful for API test scenarios
- Creating request bodies for Postman or automated tests
- Preparing mock customer, account, or order records
- Testing required fields, enums, arrays, and nested objects
- Generating repeatable payload shapes for regression testing
Learn the workflow
Follow the OpenAPI test data generation guide for examples and common schema mistakes.
Then use the REST API response comparison tool to validate behavior, or read how to test a REST API step by step.
Test data generator questions
Can I generate JSON from an OpenAPI YAML file?
Yes. Paste an OpenAPI JSON or YAML specification, choose a schema under components.schemas, and select the number of records.
Which OpenAPI schema features are supported?
The generator handles common object properties, arrays, selected formats, enums, examples, inclusive numeric ranges, string and array sizes, and local $ref links. Complex constraints such as oneOf, allOf, pattern, and multipleOf need a checked example or a simpler schema. This is a fixture generator, not a complete OpenAPI validator.
Is generated data safe for production?
The output is synthetic test data. Review it before use and never treat generated names, addresses, identifiers, or values as verified real-world information.