JSON Mock Generator

A JSON mock generator hands you a ready-to-use sample of structured JSON that matches a common API shape - a user object, a product, a generic API envelope - so you can paste it straight into a Postman collection, a Mock Service Worker handler, or a unit-test fixture without writing the structure from scratch each time.

This generator is intentionally template-first rather than schema-first. The source above defines three canonical shapes (User, Product, API Response) hand-picked because they cover the 80/20 of API contract patterns: a domain entity with timestamps, a domain entity with prices and tags, and a wrapper response with success / data / timestamp envelope fields. Click a button and the generator stringifies the corresponding object via JSON.stringify(template, null, 2) - the same pretty-printed two-space-indent output you'd get from your formatter.

Where this fits in the wider tooling landscape: heavyweight schema-driven generators like Mockaroo, JSON Schema Faker, or Faker.js let you declare arbitrary field shapes and produce thousands of records. They're the right answer when you need 10,000 unique users for load testing or want randomized data driven by an OpenAPI schema. This tool is the right answer when you need three lines of representative JSON in 10 seconds and don't want to learn a DSL first.

Each template uses live JavaScript values: new Date().toISOString() produces an ISO 8601 UTC timestamp every time you click (not a frozen literal), and Date.now() emits the current Unix milliseconds. That means two clicks 30 seconds apart produce slightly different timestamps - useful when you need fresh fixtures and don't want one stale snapshot to drift through your tests.

The User template includes id, name, email, role, and createdAt. ISO 8601 timestamps are the default for new APIs because they're unambiguous (UTC marker, sub-second precision), sortable as plain strings, and parseable by every JSON-aware language. The Product template includes a price as a JavaScript number - which is the standard JSON convention but worth noting that for currency you often want strings or integers in cents to avoid IEEE 754 floating-point rounding (29.99 + 0.01 isn't exactly 30 in any language).

The API Response template demonstrates the standard envelope pattern: a success boolean, a data field for the actual payload, and a timestamp. JSON:API, JSend, and Google's API design guide all use a variant of this. Including the envelope in your fixtures from day one prevents the "we built half our frontend assuming response.foo and now the API uses response.data.foo" refactor that costs every team a sprint.

Output is plain editable text - paste it back into the textarea, modify any field, and copy the result. There's no validation step on edit, so you can break the JSON deliberately for testing your error handling. For tighter validation, run the modified output through the JSON Formatter tool, which uses JSON.parse and surfaces the precise offset of the first syntax error.