Generate fake data from a JSON Schema

About this tool

JSON Schema Faker generates synthetic records from a JSON Schema subset. It is useful when you need repeatable fixtures for API tests, demos, import pipelines, or validation examples, but you do not want to hand-write sample rows.

Paste a schema, set a count and seed, and choose JSON array, JSON Lines, or CSV output. The same seed produces the same data, so failing tests are easy to reproduce. Everything runs locally in the browser.

Supported schema subset

• Root schemas should be objects when you want CSV; JSON and JSONL can also emit arrays or scalar roots.
• Supported types: string, integer, number, boolean, array, object, and null.
• Supported constraints: properties, required, enum, const, minLength, maxLength, minimum, maximum, minItems, and maxItems.
• Supported string formats: email, uuid, date, date-time, uri, and ipv4. Unknown formats fall back to a plain string because JSON Schema treats format as an annotation unless a validator opts in.
• Unsupported assertion constructs such as $ref, oneOf, anyOf, allOf, pattern, patternProperties, dependencies, and conditionals are rejected with a clear error instead of being silently ignored.

Worked example

Schema:

{
  "type": "object",
  "properties": {
    "id": { "type": "integer", "minimum": 1, "maximum": 99 },
    "email": { "type": "string", "format": "email" },
    "role": { "enum": ["admin", "user", "guest"] }
  },
  "required": ["id", "email"]
}

With count = 3, seed = 42, and output = json, the tool returns a JSON array of three object records with numeric IDs, email-shaped strings, and roles chosen from the enum.

Limits & edge cases

• Record count is capped at 1000 to keep browser, chat, and CLI output bounded.
• CSV output requires object rows. Nested objects or arrays are serialized into a single CSV cell as compact JSON.
• The generator emits every defined property, so required fields are always present. It does not invent extra properties.
• multipleOf, custom faker providers, cross-field dependencies, and $ref resolution are intentionally out of scope for this pure local block.

FAQ