Mock Data Generator

Generate realistic fake JSON from a sample or schema — infers types, patterns and ranges. Output any number of records to seed databases and test APIs.

Records From Indent

Input

Generated

How it works

Sample mode — paste one real record and the tool infers the type, range, and pattern of every field. Email fields become random emails, age fields become integers in the same range, boolean fields flip randomly.
Schema mode — paste a JSON Schema (draft-07 / 2020-12) and every constraint is honored: enums stay within their options, strings respect minLength/maxLength/pattern, numbers respect minimum/maximum/multipleOf, and required properties are never omitted.
Output is a JSON array with the requested number of records — ready to paste into your test suite or import script.

Sample mode infers from keys, not just values

In sample mode each field is inspected twice — once by property name, once by the shape of the value. A key containing `name` yields a full name, one containing `email` yields a synthesised address, `phone` or `tel` yields a formatted number, `company` or `org` yields a company name, and a long string under a key containing `id` becomes a generated identifier. Value-shape detection then handles whatever the key heuristics miss.

Numbers are generated near the sample value rather than across a wide range: the spread is half the sample magnitude with a floor of one, clamped to stay on the same side of zero. A sample of 100 yields values between 50 and 150, while a sample of 0 yields only 0 or 1 — a real limitation for fields that should span a wider domain. Arrays generate one to five elements using the first element as a template.

Schema mode and the constraints it honours

Schema mode walks the schema directly: `enum` picks a random member, `const` is emitted verbatim, and the declared type drives generation. String formats email, date, date-time and uri produce matching synthetic values, and numeric `minimum`, `maximum` and `multipleOf` are respected, with the multiple rounded after the random draw. Defaults are −1000 and 1000 when no bounds are given.

Objects emit every declared property, required or not. Required fields are always present and optional ones appear roughly seventy percent of the time, which gives realistic sparsity without producing records missing too much. A schema-level `additionalProperties` object contributes one to three extra keys with random four-character suffixes.

Limits worth knowing

String length constraints are approximated rather than enforced. The word count is derived from `maxLength` by dividing by five or four, so `maxLength: 3` can still yield a string around twelve characters, and `minLength` is not consulted at all. `pattern` is ignored in schema mode entirely, so a constrained string will not reliably match its own regex.

Generated identifiers are UUID-shaped with the version nibble correctly set to `4`, but the variant nibble is left random, so roughly three quarters of them fail strict RFC 4122 validation — fine for fixtures, not for a test asserting format compliance. Generated dates always fall in the past, up to about ten years back. Record count is capped at 500, and the random source is unseeded, so two runs over identical input will differ.

Frequently Asked Questions

How do I generate mock JSON data?

There are two modes: Sample mode — paste one real JSON record and the tool automatically infers the type, range, and pattern of every field (email fields become random emails, numbers stay in the same range). Schema mode — paste a JSON Schema and the tool generates data that satisfies every constraint. Click Generate and pick how many records to produce.

What types of mock data are available?

The tool generates realistic fake data including names, emails, phone numbers, addresses, dates, UUIDs, credit card numbers, URLs, lorem ipsum text, and more. All generated data is structurally consistent with your schema.

Is my data sent to a server?

No. Every tool on jsonversal runs entirely in your browser using the Web Crypto API, File API, and Clipboard API. Nothing is ever uploaded — not even the JSON you paste in.

Do I need an account or API key?

No signup, no email, no API key. All tools are free to use with no signup required.

Can I use these tools offline?

Yes. Once the page loads, all tools work offline. There are no external API calls or CDN dependencies at runtime.

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Your data never leaves your device

All processing happens in your browser. No uploads, no tracking, no servers. Your API keys, configs, and private payloads stay private — 100% client-side.