Generate a sample JSON instance from a JSON Schema

About this tool

This tool turns a JSON Schema into the smallest JSON document that satisfies it. Paste a schema, and you get an example instance you can drop straight into API documentation, a test fixture, a mock response, or a request body you are about to send by hand.

It is deliberately minimal, not random: by default only required properties appear (plus any property that declares a default), every value is derived from the schema itself, and the same schema always produces the same output. Nothing is uploaded — the schema is parsed and the sample built inside your browser.

Tick Include optional properties when you want the full shape instead, raise Array items to show more than one entry per array, and untick Pretty-print for a single compact line.

Where each value comes from

Values are taken from the first of these the schema provides, in order:

1. const — the only value the schema allows.
2. default — the documented fallback value.
3. examples[0], or OpenAPI 3.0's singular example.
4. enum[0] — the first accepted choice.
5. A value generated from type and format.

So a schema that already documents itself with default/examples gets your values back, not invented ones.

Supported schema keywords

• Types: object, array, string, integer, number, boolean, null, union types such as ["string", "null"] (the first non-null member wins), and the boolean schemas true / false.
• Objects: properties, required, additionalProperties as a schema.
• Arrays: items, prefixItems, draft-07 tuple items: [...] with additionalItems, minItems, maxItems, uniqueItems.
• Strings: minLength, maxLength, and format — email, uuid, date, date-time, time, duration, uri, uri-reference, uri-template, hostname, ipv4, ipv6, byte, json-pointer, regex. Unknown formats fall back to a plain string, because format is an annotation unless a validator opts in.
• Numbers: minimum, maximum, exclusiveMinimum, exclusiveMaximum (both the draft-04 boolean form and the numeric form), multipleOf.
• Composition: allOf is deep-merged; oneOf / anyOf use the first branch.
• References: local $ref pointers into the same document — #/$defs/Name, #/definitions/Name, or any JSON pointer such as #/properties/user. Recursive schemas stop at the first repeat with null.

Drafts 07, 2019-09 and 2020-12 all work; the tool reads the keywords that are present rather than requiring a $schema declaration.

Worked example

Schema:

{
  "type": "object",
  "properties": {
    "id": { "type": "integer", "minimum": 1 },
    "email": { "type": "string", "format": "email" },
    "nickname": { "type": "string" }
  },
  "required": ["id", "email"]
}

Sample JSON (defaults: optional properties off, one array item, pretty-printed):

{
  "id": 1,
  "email": "[email protected]"
}

nickname is optional, so it is left out. id becomes 1 because minimum: 1 is the smallest allowed integer, and email is shaped by its format.

Tick Include optional properties and nickname joins the sample as "string".

Limits & edge cases

• The schema must be at most 1 MB, and generation stops after 50,000 values — lower Array items or untick Include optional properties if you hit that on a very wide schema.
• Array items accepts 0–50. A larger minItems always wins, and maxItems still caps the result, so bounded arrays stay valid.
• Length assertions beat format: with minLength/maxLength set, the string is padded or truncated even if that spoils an email or UUID shape, because length is an assertion while format is an annotation.
• Recursive $ref chains are cut at the first repeat and nesting stops after 32 levels; both emit null at the cut point rather than looping forever.
• Remote $refs (https://…/schema.json#/…) are rejected with a clear error — there is no network fetch in a browser-local tool. Inline your definitions under $defs first.
• Not synthesised, and reported rather than faked where it matters: pattern, patternProperties, not, if/then/else, dependentSchemas, dependencies, propertyNames, contains, minProperties/maxProperties, and readOnly/writeOnly filtering. A schema whose validity rests only on pattern may need a manual touch-up.
• A schema of false accepts no instance at all, so it returns an error instead of a sample.

FAQ