Lee Johnson


JSON::Schema::ToJSON - Generate example JSON structures from JSON Schema definitions




    use JSON::Schema::ToJSON;

    my $to_json  = JSON::Schema::ToJSON->new(
        example_key => undef, # set to a key to take example from
        max_depth   => 10,    # increase if you have very deep data structures

    my $perl_string_hash_or_arrayref = $to_json->json_schema_to_json(
        schema     => $already_parsed_json_schema,  # either this
        schema_str => '{ "type" : "boolean" }',     # or this


JSON::Schema::ToJSON is a class for generating "fake" or "example" JSON data structures from JSON Schema structures.



The key that will be used to find example data for use in the returned structure. In the case of the following schema:

        "type" : "object",
        "properties" : {
            "id" : {
                "type" : "string",
                "description" : "ID of the payment.",
                "x-example" : "123ABC"

Setting example_key to x-example will make the generator return the content of the "x-example" (123ABC) rather than a random string/int/etc. This is more so for things like OpenAPI specifications.

You can set this to any key you like, although be careful as you could end up with invalid data being used (for example an integer field and then using the description key as the content would not be sensible or valid).


To prevent deep recursion due to circular references in JSON schemas the module has a default max depth set to a very conservative level of 10. If you need to go deeper than this then pass a larger value at object construction.



    my $perl_string_hash_or_arrayref = $to_json->json_schema_to_json(
        schema     => $already_parsed_json_schema,  # either this
        schema_str => '{ "type" : "boolean" }',     # or this

Returns a randomly generated representative data structure that corresponds to the passed JSON schema. Can take either an already parsed JSON Schema or the raw JSON Schema string.


Caveats? The implementation is incomplete as using some of the more edge case JSON schema validation options may not generate representative JSON so they will not validate against the schema on a round trip. These include:

  • additionalItems

    This is ignored

  • additionalProperties and patternProperties

    These are also ignored

  • dependencies

    This is *also* ignored, possible result of invalid JSON if used

  • oneOf

    Only the *first* schema from the oneOf list will be used (which means that the data returned may be invalid against others in the list)

  • not

    Currently any not restrictions are ignored as these can be very hand wavy but we will try a "best guess" in the case of "not" : { "type" : ... }

In the case of oneOf and not the module will raise a warning to let you know that potentially invalid JSON has been generated. If you're using this module then you probably want to avoid oneOf and not in your schemas.

It is also entirely possible to pass a schema that could never be validated, but will result in a generated structure anyway, example: an integer that has a "minimum" value of 2, "maximum" value of 4, and must be a "multipleOf" 5 - a nonsensical combination.

Note that the data generated is completely random, don't expect it to be the same across runs or calls. The data is also meaningless in terms of what it represents such that an object property of "name" that is a string will be generated as, for example, "kj02@#fjs01je#$42wfjs" - The JSON generated is so you have a representative structure, not representative data. Set example keys in your schema and then set the example_key in the constructor if you want this to be repeatable and/or more representative.


This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. If you would like to contribute documentation, features, bug fixes, or anything else then please raise an issue / pull request:



Lee Johnson - leejo@cpan.org