json-schema-gen-cli

Generate JSON Schema (Draft-7) from sample JSON data automatically. No external dependencies.

Install

npm install -g json-schema-gen-cli

Usage

json-schema-gen <file|string> [options]
jsg             <file|string> [options]   # short alias

Examples

From a JSON file:

json-schema-gen sample.json

Save schema to a file:

json-schema-gen sample.json --output schema.json

From an inline JSON string:

json-schema-gen '{"name":"Alice","age":30}' --inline

Mark all fields as required:

json-schema-gen sample.json --required

Add a title:

json-schema-gen sample.json --title "User"

Output TypeScript interface instead:

json-schema-gen sample.json --typescript

Sample Input/Output

Input (user.json):

{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "name": "Alice",
  "age": 30,
  "score": 9.5,
  "active": true,
  "email": "[email protected]",
  "homepage": "https://alice.dev",
  "tags": ["admin", "user"],
  "address": {
    "street": "123 Main St",
    "city": "Springfield",
    "zip": "12345"
  },
  "metadata": null
}

Output (json-schema-gen user.json --title "User" --required):

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "User",
  "type": "object",
  "properties": {
    "id":       { "type": "string", "format": "uuid" },
    "name":     { "type": "string" },
    "age":      { "type": "integer" },
    "score":    { "type": "number" },
    "active":   { "type": "boolean" },
    "email":    { "type": "string", "format": "email" },
    "homepage": { "type": "string", "format": "uri" },
    "tags":     { "type": "array", "items": { "type": "string" } },
    "address": {
      "type": "object",
      "properties": {
        "street": { "type": "string" },
        "city":   { "type": "string" },
        "zip":    { "type": "string" }
      },
      "additionalProperties": false
    },
    "metadata": { "type": "null" }
  },
  "required": ["id","name","age","score","active","email","homepage","tags","address","metadata"],
  "additionalProperties": false
}

TypeScript output (json-schema-gen user.json --typescript --title "User"):

export interface User {
  id?: string;
  name?: string;
  age?: number;
  score?: number;
  active?: boolean;
  email?: string;
  homepage?: string;
  tags?: string[];
  address?: { street?: string; city?: string; zip?: string };
  metadata?: null;
}

Schema Inference Rules

| JSON Value | JSON Schema Type | |--------------------|-------------------------------| | "hello" | string | | "2024-01-01" | string + format: date-time| | "[email protected]" | string + format: email | | "https://..." | string + format: uri | | UUID string | string + format: uuid | | 42 | integer | | 3.14 | number | | true/false | boolean | | null | null | | [...] | array (items inferred) | | {...} | object (properties inferred)| | Mixed array types | anyOf union |

Options

| Flag | Short | Description | |---------------------|-------|------------------------------------------| | --output <file> | -o | Write output to file | | --inline | -i | Treat argument as inline JSON string | | --required | -r | Mark all object properties as required | | --title <name> | | Add title field to schema | | --typescript | -t | Output TypeScript interface | | --help | -h | Show help |

License

MIT © Wilson Xu