Schema Generator

Generate a draft-07 JSON schema definitions from an example JSON document

Features

• Generate a draft-07 JSON schema definitions from an example JSON document
• Easy to use
• Supports string formats (with more to come)
• Can generate either a strict or liberal schema

Usage

Install Schema Generator

$ npm install --save @jsonhero/schema-generator

generateSchema takes either a JSON object/array or JSON stringified and returns a valid draft-07 JSON Schema

const { generateSchema } = require("@jsonhero/schema-generator");

const exampleJSON = {
  id: 1234,
  name: "Eric",
  image: {
    url: "https://foo.com/image.png",
  },
  email: "[email protected]",
  homepage: "http://github.com/ericallam",
  createdAt: "2021-12-17T12:55:58.141Z",
  tags: ["foo", "bar"],
  isAdmin: true,
};

const schema = generateSchema(exampleJSON);

// Now validate the provided JSON using the generated schema using ajv
const Ajv = require("ajv");
const ajv = new Ajv();
const addFormats = require("ajv-formats");
addFormats(ajv);

const validate = ajv.compile(schema);
const valid = validate(exampleJSON); // valid == true

The Schema generated in the above example

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://jsonhero.io/schemas/root.json",
  "type": "object",
  "properties": {
    "id": {
      "type": "number"
    },
    "name": {
      "type": "string"
    },
    "image": {
      "type": "object",
      "properties": {
        "url": {
          "type": "string",
          "format": "uri"
        }
      },
      "required": [],
      "additionalProperties": true
    },
    "email": {
      "type": "string",
      "format": "email"
    },
    "homepage": {
      "type": "string",
      "format": "uri"
    },
    "createdAt": {
      "type": "string",
      "format": "date-time"
    },
    "tags": {
      "type": "array",
      "items": {
        "type": "string"
      }
    },
    "friends": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "id": {
            "type": "number"
          },
          "name": {
            "type": "string"
          }
        },
        "required": [],
        "additionalProperties": true
      }
    },
    "isAdmin": {
      "type": "boolean"
    }
  },
  "required": [],
  "additionalProperties": true
}

By default all properties are optional and additionalProperties are allowed. You can set the strict option to true if you'd like a more restrictive schema

const { generateSchema } = require("@jsonhero/schema-generator");

const exampleJSON = {
  id: 1234,
  name: "Eric",
  image: {
    url: "https://foo.com/image.png",
  },
  email: "[email protected]",
  homepage: "http://github.com/ericallam",
  createdAt: "2021-12-17T12:55:58.141Z",
  tags: ["foo", "bar"],
  isAdmin: true,
};

const schema = generateSchema(exampleJSON, { strict: true });

// Now validate the provided JSON using the generated schema using ajv
const Ajv = require("ajv");
const ajv = new Ajv();
const addFormats = require("ajv-formats");
addFormats(ajv);

const validate = ajv.compile(schema);
const valid = validate(exampleJSON); // valid == true

The Schema generated in the above example

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://jsonhero.io/schemas/root.json",
  "type": "object",
  "properties": {
    "id": {
      "type": "number"
    },
    "name": {
      "type": "string"
    },
    "image": {
      "type": "object",
      "properties": {
        "url": {
          "type": "string",
          "format": "image"
        }
      },
      "required": ["url"],
      "additionalProperties": false
    },
    "email": {
      "type": "string",
      "format": "email"
    },
    "homepage": {
      "type": "string",
      "format": "uri"
    },
    "createdAt": {
      "type": "string",
      "format": "date-time"
    },
    "tags": {
      "type": "array",
      "items": {
        "type": "string"
      }
    },
    "friends": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "id": {
            "type": "number"
          },
          "name": {
            "type": "string"
          }
        },
        "required": ["id", "name"],
        "additionalProperties": false
      }
    },
    "isAdmin": {
      "type": "boolean"
    }
  },
  "required": [
    "id",
    "name",
    "image",
    "email",
    "homepage",
    "createdAt",
    "tags",
    "friends",
    "isAdmin"
  ],
  "additionalProperties": false
}

Generate Schema currently supports a few string formats

• Strings that are URLs will have the uri format
• Strings that are Date/Times will have the date-time format
• Strings that are emails will have the email format

If you are using ajv to use the generated schema, make sure to use the ajv-formats package

const addFormats = require("ajv-formats");
addFormats(ajv);

You can also set the baseURI of the schema (i.e. the top level $id property)

const { generateSchema } = require("@jsonhero/schema-generator");

const exampleJSON = {
  foo: "bar",
};

const schema = generateSchema(exampleJSON, {
  baseURI: "https://example.com/schemas/root.json",
});

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://example.com/schemas/root.json",
  "type": "object",
  "properties": {
    "foo": {
      "type": "string"
    }
  },
  "required": [],
  "additionalProperties": true
}

Roadmap

• [ ] Support more draft versions of JSON Schema
• [ ] Support JSON Type Definitions
• [ ] Support enums and constants
• [ ] Support more string formats (regex, ipv4, ipv6, hostname, JSONPointer, time, date, uuid)
• [ ] Add examples