JSON Schema Faker vs Mockaroo

JSON Schema Faker generates synthetic JSON data from JSON Schema definitions. It supports JSON Schema 2019-09 and 2020-12, and a numeric seed can make results repeatable. The `jsf` command can read schema files, save generated JSON to a file, and produce multiple items as an array. Reference support includes `$ref` resolution with cycle detection, adjustable recursion depth, and remote reference resolution. Built-in generators cover formats such as email, date-time, URI, IP addresses, and UUID; regex patterns are supported through an AST-based string generator. Users can register custom formats and keyword generators, with optional extensions for faker.js and chance.js. YAML output requires the YAML package through an extension. The project runs in Node.js and browsers and is built for Bun and Node.js. It is self-hosted and open source under the MIT License, with zero production dependencies. The listed plan costs nothing. One constraint: synchronous generation works only when schemas resolve without I/O; asynchronous resolvers or extensions cause it to throw.

Mockaroo is a web-based synthetic data generator for developers and testers who need realistic test records or a mock back end while building a user interface. It offers more than 100 built-in data types; users can also upload reference data or define types with the formula API. The Generate API produces JSON, CSV, tab-separated or custom-delimited text, SQL, and XML. Mock APIs can connect request parameters to schemas and return dynamic or static data, or simulate errors. Both APIs require an API key, sent as a query parameter or an X-API-Key header. Free includes 1,000 rows per file and 200 API requests per day. Silver is $60 a year and allows 100,000 rows per file and 1 million API records per day; Gold is $500 a year and allows 10 million rows per file and 10 million API records per day. Synchronous API responses are limited to 5,000 records on every plan; background generation requires a paid plan. Enterprise is $7,500 a year, with unlimited data and users and Docker deployment in a private cloud or datacenter.