json-schema-gen

Generate JSON Schema (draft-07) from sample JSON data. Detects string formats (email, URI, UUID, date-time), merges schemas from multiple samples, and outputs a clean schema ready for validation. Zero dependencies.

Like quicktype but needs no installation — and genson (Python) or online tools are overkill when you just need a schema.

Install

npm install -g json-schema-gen

Or without installing:

npx json-schema-gen data.json

Example

Given user.json:

{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "name": "Alice Johnson",
  "email": "[email protected]",
  "age": 32,
  "active": true,
  "createdAt": "2024-01-15T09:30:00Z",
  "tags": ["admin", "user"],
  "address": {
    "street": "123 Main St",
    "city": "Springfield",
    "zip": "62701"
  }
}

Running json-schema-gen user.json --required outputs:

{
  "$schema": "https://json-schema.org/draft-07/schema",
  "type": "object",
  "properties": {
    "id":        { "type": "string", "format": "uuid" },
    "name":      { "type": "string" },
    "email":     { "type": "string", "format": "email" },
    "age":       { "type": "integer" },
    "active":    { "type": "boolean" },
    "createdAt": { "type": "string", "format": "date-time" },
    "tags":      { "type": "array", "items": { "type": "string" } },
    "address": {
      "type": "object",
      "properties": {
        "street": { "type": "string" },
        "city":   { "type": "string" },
        "zip":    { "type": "string" }
      },
      "required": ["street", "city", "zip"],
      "additionalProperties": false
    }
  },
  "required": ["id", "name", "email", "age", "active", "createdAt", "tags", "address"],
  "additionalProperties": false
}

Usage

json-schema-gen user.json                            # Basic schema
json-schema-gen user.json --required                 # Mark all fields as required
json-schema-gen user.json --title "User" --id "/schemas/user"
json-schema-gen user.json --out schema.json          # Write to file
json-schema-gen s1.json s2.json s3.json              # Merge from multiple samples
cat data.json | json-schema-gen -                    # Read from stdin

Detected Formats

| Format | Example | |---|---| | date-time | "2024-01-15T09:30:00Z" | | date | "2024-01-15" | | time | "09:30:00" | | email | "[email protected]" | | uri | "https://example.com" | | uuid | "a1b2c3d4-e5f6-7890-abcd-ef1234567890" | | ipv4 | "192.168.1.1" |

Multi-Sample Merging

Pass multiple JSON files to infer a schema that covers all of them. Fields present in only some samples will not be marked required:

json-schema-gen user1.json user2.json user3.json

Options

| Flag | Description | |---|---| | --required | Mark all non-null fields as required | | --examples | Include example values for string fields | | --title <name> | Add title to the schema | | --id <uri> | Add $id to the schema | | --out <file> | Write output to a file |

License

MIT

Keywords

json schema generator · json to schema · quicktype alternative · genson alternative · infer schema · draft-07 · generate schema · json schema · zero dependencies · cli

Built to solve, shared to help — Rushabh Shah 🛠️✨

One of 40+ zero-dependency developer CLI tools — no node_modules, ever.