@toolsycc/json-schema-gen

A tiny and focused utility to generate lightweight JSON Schema objects, especially for OpenAI Function Calling or structured output.
✅ Works with both TypeScript and JavaScript (ESM & CommonJS).

Features

• Build clean JSON Schema from simple JS object structure
• Support for:
  • basic types: string, number, integer, boolean, object, array
  • optional description per field
  • required fields detection
  • nested object schemas
  • arrays with items definitions
• Minimal and dependency-free
• Output is compatible with OpenAI functions and tool_choice: "auto"

Install

pnpm add @toolsycc/json-schema-gen

Or with npm:

npm install @toolsycc/json-schema-gen

Example usage

🟦 TypeScript

import { generateSchema } from '@toolsycc/json-schema-gen';

const schema = generateSchema({
  name: { type: "string", description: "User name", required: true },
  age: { type: "integer", description: "User age" },
});

console.log(schema);
/*
{
  type: "object",
  properties: {
    name: { type: "string", description: "User name" },
    age: { type: "integer", description: "User age" }
  },
  required: ["name"]
}
*/

🟨 JavaScript (CommonJS)

const { generateSchema } = require('@toolsycc/json-schema-gen');

const schema = generateSchema({
  id: { type: "string", required: true },
  tags: { type: "array", items: { type: "string" } }
});

console.log(schema);

🟩 JavaScript (ESM)

import { generateSchema } from '@toolsycc/json-schema-gen';

const schema = generateSchema({
  enabled: { type: "boolean", description: "Whether the feature is active" }
});

console.log(schema);

🔁 Generate schema from real JSON data

You can generate a schema directly from a plain JavaScript object using generateSchemaFromData.

import { generateSchemaFromData } from '@toolsycc/json-schema-gen';

const data = {
  name: "Seb",
  age: 42,
  active: true,
  tags: ["dev", "founder"],
  address: {
    city: "Bordeaux",
    zip: "33000"
  }
};

const schema = generateSchemaFromData(data);
console.log(schema);

/*
{
  type: "object",
  properties: {
    name: { type: "string" },
    age: { type: "integer" },
    active: { type: "boolean" },
    tags: {
      type: "array",
      items: { type: "string" }
    },
    address: {
      type: "object",
      properties: {
        city: { type: "string" },
        zip: { type: "string" }
      },
      required: ["city", "zip"]
    }
  },
  required: ["name", "age", "active", "tags", "address"]
}
*/

✅ Validate your data against a schema

You can also validate any data against a JSON Schema using validateSchema.

import { validateSchema } from '@toolsycc/json-schema-gen';

const schema = {
  type: "object",
  properties: {
    name: { type: "string" },
    age: { type: "integer" },
    tags: { type: "array", items: { type: "string" } }
  },
  required: ["name", "age"]
};

const data = {
  name: "Seb",
  age: "not-a-number",
  tags: ["dev", "founder"]
};

const result = validateSchema(schema, data);
console.log(result.valid); // false
console.log(result.errors); // ['"age" should be an integer']

Motivation

This package was designed to help generate valid JSON Schema definitions, especially in the context of OpenAI’s structured outputs or function calling APIs.
It aims to provide a minimal abstraction with clean output and zero dependencies.

Author

Made by @Sebog33
Follow Toolsy for more tiny dev-focused utilities.

License

MIT