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Mock API Generator

Generate realistic fake JSON data from a JSON Schema, OpenAPI 3.x spec, or a sample JSON object shape.

JSON Schema OpenAPI 3.x Smart field names No signup

How the Mock API Generator Works

The ByteKiln Mock API Generator parses JSON Schema or OpenAPI specs in-browser and generates realistic fake data using a lightweight built-in data generator with no external faker dependency.

Schema walking

The tool recursively walks the JSON Schema, handling type, properties, items, enum, anyOf, oneOf, allOf, const, and format keywords. Each leaf node generates a typed fake value.

Smart string generation

String fields without a format annotation are classified by field name. Names containing "email", "url", "id", "name", "phone", "date", "status", "color", or "slug" each produce contextually appropriate fake values.

OpenAPI parsing

For OpenAPI specs, the tool iterates all paths and HTTP methods, finds the 2xx response schema, resolves any $ref pointers, and generates mock data for each endpoint.

Read the full guide

FAQ

Short answers for the things developers usually ask before trusting a tool.

What input formats are supported?

Three input modes are supported: a sample JSON object (the shape is inferred), a JSON Schema (Draft 7 compatible), and an OpenAPI 3.x spec (JSON format). The tool auto-detects which mode to use.

How is the fake data generated?

The generator uses a seeded pseudo-random number generator. String values are generated based on the field name — a field named "email" produces an email address, "createdAt" produces an ISO timestamp, and "id" produces a UUID.

Does it support nested objects and arrays?

Yes. The schema walker handles object types with nested properties, array types with items schemas, anyOf/oneOf/allOf combiners, and enum values. Recursion is limited to a depth of 6 to prevent infinite loops.

Are $ref schemas resolved?

Same-document $ref references (e.g. #/components/schemas/User in an OpenAPI spec) are resolved by traversing the JSON path. External file references are not supported.

Can I use this to generate test fixtures?

Yes. Download the JSON output and use it directly as fixture data in Jest, Vitest, Playwright, or any testing framework. Set the record count to the number of test cases you need.

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formatters