JSON Schema Builder

A TypeScript library and CLI tool to generate JSON schemas from sample JSON data. Supports complex nested objects, arrays, and automatic format detection.

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Installation

Global Installation (CLI)

npm install -g jssb-cli

Local Installation (Library)

npm install jssb-cli

CLI Usage

After global installation, use the jssb command:

# Basic usage - generates input-name.schema.json
jssb data.json

# Specify custom output file
jssb data.json --output my-schema.json

# With custom title and options
jssb data.json --title "User Schema" --no-examples --infer-enums

CLI Options

Option	Short	Description	Default
--output	-o	Output file path	<input-name>.schema.json
--title	-t	Schema title	Derived from filename
--no-examples		Exclude examples from schema	Include examples
--no-format		Disable format detection	Format detection enabled
--no-required		Don't mark properties as required	Mark as required
--additional-props		Allow additional properties	Disallow additional properties
--infer-enums		Enable enum inference	Disabled
--enum-threshold		Max unique values for enums	5
--help	-h	Show help message

CLI Examples

# Generate schema for user data
jssb user.json

# Custom output location
jssb data/users.json --output schemas/user.schema.json

# With enum detection for repeated values
jssb config.json --infer-enums --enum-threshold 3

# Minimal schema without examples
jssb api-response.json --no-examples --title "API Response"

Library Usage

import { JsonSchemaBuilder } from 'jsonschema-builder';

const builder = new JsonSchemaBuilder({
  includeExamples: true,
  detectFormat: true,
  requiredByDefault: true,
  additionalProperties: false
});

const sampleData = {
  name: 'John Doe',
  age: 30,
  email: 'john@example.com',
  hobbies: ['reading', 'coding']
};

const schema = builder.build(sampleData, 'User');
console.log(JSON.stringify(schema, null, 2));

Features

• ✅ Complex nested objects - Handles deep nesting and complex structures
• ✅ Array support - Mixed types, nested arrays, unique item detection
• ✅ Format detection - Email, URL, date, UUID, IP addresses
• ✅ Multiple samples - Build schemas from multiple JSON samples
• ✅ Enum inference - Detect repeated values and create enums
• ✅ Type validation - Strict TypeScript types
• ✅ CLI tool - Easy command-line usage
• ✅ Configurable - Many options to customize output

Supported Formats

• email - user@example.com
• uri - https://example.com
• date - 2024-01-15
• date-time - 2024-01-15T10:30:00.000Z
• uuid - 550e8400-e29b-41d4-a716-446655440000
• ipv4 - 192.168.1.1
• ipv6 - 2001:0db8:85a3:0000:0000:8a2e:0370:7334

Configuration Options

interface SchemaBuilderOptions {
  includeExamples?: boolean;     // Include sample values (default: true)
  detectFormat?: boolean;        // Auto-detect string formats (default: true)
  requiredByDefault?: boolean;   // Mark properties as required (default: true)
  additionalProperties?: boolean; // Allow additional properties (default: false)
  inferEnums?: boolean;          // Detect enum patterns (default: false)
  enumThreshold?: number;        // Max unique values for enums (default: 5)
}

Examples

Input JSON

{
  "id": "550e8400-e29b-41d4-a716-446655440000",
  "user": {
    "name": "John Doe",
    "email": "john@example.com",
    "createdAt": "2024-01-15T10:30:00.000Z"
  },
  "tags": ["premium", "verified"]
}

Generated Schema

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "title": "User",
  "properties": {
    "id": {
      "type": "string",
      "format": "uuid"
    },
    "user": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "email": { "type": "string", "format": "email" },
        "createdAt": { "type": "string", "format": "date-time" }
      },
      "required": ["name", "email", "createdAt"],
      "additionalProperties": false
    },
    "tags": {
      "type": "array",
      "items": { "type": "string" },
      "uniqueItems": true
    }
  },
  "required": ["id", "user", "tags"],
  "additionalProperties": false
}

Development

# Install dependencies
npm install

# Build TypeScript
npm run build

# Run examples
npm run example

# Link for local testing
npm link

License

MIT