JSON Schema Faker Skill

Generate realistic fake data from JSON schemas with guaranteed validity.

Quick Start

When you have a JSON schema and need realistic sample data:

node scripts/generate-fake-data.mjs /path/to/schema.json 25

This generates 25 valid records conforming to your schema.

Requirements

Install dependencies first:

npm install @json-schema-faker/core ajv

How It Works

1. Parse schema - Loads and validates your JSON schema
2. Configure faker - Sets up realistic data generation with custom rules
3. Generate records - Creates 1-50 records using faker
4. Validate output - Validates each record against the schema
5. Return JSON - Outputs only valid records as pretty-printed JSON

Features

Schema Compliance: All generated records are validated against the schema—only valid JSON is returned.

Realistic Data: Uses faker.js with domain-specific extensions (currency codes, country codes, time windows) to produce realistic data beyond simple random strings.

Customizable: Specify 1-50 records. Script auto-caps at 50.

Error Handling: Handles generation failures gracefully; reports warnings for records that couldn't be generated after multiple attempts.

Usage

Basic Generation

node scripts/generate-fake-data.mjs schema.json 10

Generates 10 records from

schema.json

, outputs JSON to stdout.

Specify Record Count

node scripts/generate-fake-data.mjs schema.json 50

Records are capped at 50 maximum. If omitted, defaults to 10.

Save to File

node scripts/generate-fake-data.mjs schema.json 30 > output.json

Improving Data Quality

The faker library generates realistic data based on schema hints. To improve data quality:

1. Add format hints: Use

   "format": "email"

   ,

   "format": "date"

   ,

   "format": "uri"

2. Add faker directives: Use

   "faker": "name.firstName"

   to guide generation
3. Use enums: For constrained fields, provide valid options
4. Set constraints: Use

   minimum

   ,

   maximum

   ,

   minLength

   ,

   maxLength

   appropriately
5. Avoid overly restrictive patterns: Very complex regex patterns may cause generation to fail

See

references/faker-customization.md

for detailed customization options and available faker methods.

Example: Accommodation Listings

Given a schema for accommodation listings (with faker hints for currency and country), the skill generates realistic data like:

[
  {
    "id": "listing_ashdod_001",
    "title": "Beachfront Apartment",
    "type": "apartment",
    "location": {
      "city": "Ashdod",
      "countryCode": "IL",
      "distanceToBeachMinutes": 5,
      "coordinates": { "lat": 31.8, "lng": 34.65 }
    },
    "rating": { "score": 8.5, "count": 45 },
    "pricePreview": {
      "currency": "USD",
      "nightly": 180,
      "total": 540,
      "nights": 3
    },
    ...
  }
]

Troubleshooting

"Could not generate valid record": The schema may have constraints that conflict (e.g., minLength > maxLength). Review your schema constraints.

"Failed to parse schema": Ensure the schema file is valid JSON.

Too few records generated: Some schemas have tight constraints. Increase attempts or relax schema constraints.

Advanced Customization

To add custom faker methods beyond the built-in ones (currencyCode, countryCode, timeWindow), edit the

setupFaker()

function in

scripts/generate-fake-data.mjs

.

Example: Add a custom "accommodationType" method:

faker.accommodationType = () => {
  const types = ['apartment', 'house', 'hotel', 'bnb']
  return faker.random.arrayElement(types)
}

Then use in your schema:

{
  "type": "string",
  "faker": "accommodationType"
}