JSON Schema Faker
Generate realistic mock JSON data from JSON Schema (Draft 2020-12 and draft-07) with seeded determinism, format-aware strings, enums, refs, and JSONL export -
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What is JSON Schema Faker?
The JSON Schema Faker turns a JSON Schema definition into realistic sample JSON documents. It parses Draft 2020-12 and draft-07 keywords, resolves internal references, honors types, enums, formats, patterns, and numeric constraints, and produces as many mock records as you need - all offline in your browser.
Key Benefits
- Instant test fixtures that satisfy your schema contract
- Reproducible output via seeded generation
- Realistic emails, UUIDs, dates, and IPs from format keywords
- JSON and JSONL export for APIs and AI pipelines
- Private - schemas never leave your machine
Common Use Cases
- •Seeding API stubs and mock servers during development
- •Generating snapshot-test fixtures that match a schema
- •Preparing demo data for UI prototypes and dashboards
- •Building JSONL training sets for LLM fine-tuning
- •QA datasets with valid enum values, ranges, and formats
How to Use the JSON Schema Faker
- Paste your schema: Copy a JSON Schema object (Draft 2020-12, 2019-09, or draft-07) and paste it into the input box, or click Load Example Schema to try a ready-made user schema.
- Set generation options: Choose how many documents to generate (1-100). Optionally enter a seed for reproducible output, and toggle example/default precedence and format detection.
- Generate mock data: Click Generate Mock Data. The tool validates your schema, resolves refs, and renders sample documents that satisfy every constraint.
- Copy or export: Copy the JSON to your clipboard, download it as a formatted .json file, or export JSONL/NDJSON for AI training sets and streaming pipelines.
Key Features
- Draft 2020-12, 2019-09, and draft-07 keyword support, including prefixItems and tuple items
- Internal $ref resolution to $defs and definitions, plus allOf merging and anyOf/oneOf branch selection
- Example and default precedence - reuse the sample values already written in your schema
- Seedable PRNG for fully reproducible mock data and shareable seeds across teams
- Export as formatted JSON or JSONL/NDJSON for AI training sets and streaming pipelines
Frequently Asked Questions
Which JSON Schema drafts are supported?
The generator understands Draft 2020-12 and 2019-09 keywords such as prefixItems and $defs, as well as draft-07 keywords including definitions and items arrays. Unsupported keywords are simply ignored.
How do I get the same mock data every time?
Enter a seed number before generating. The same schema plus the same seed always produces identical documents - handy for snapshot tests and bug reports.
Does it respect enum, pattern, and numeric constraints?
Yes. Values are chosen from enums, strings match a subset of regular expression patterns, and numbers honor minimum, maximum, exclusive bounds, and multipleOf.
Is my schema uploaded anywhere?
No. Parsing, generation, and export all happen locally in your browser. Nothing is sent to a server, so it is safe for internal and proprietary schemas.