JSON to TypeScript Interface Generator Online

How to Use JSON to TypeScript

Paste your JSON into the input panel on the left. This can be an API response, a configuration object, a database record, or any valid JSON.
Set the root interface name using the input field above the editor. The default is “Root” but you should use a descriptive name like “User”, “ApiResponse”, or “Config”.
Click “Generate TypeScript” to produce TypeScript interfaces with inferred types for every property.
Review the output in the right panel. Each nested object gets its own interface, and arrays are properly typed.
Copy and paste the interfaces into your TypeScript project. Adjust optional fields (?) and union types as needed for your specific use case.

What is JSON to TypeScript Conversion?

JSON to TypeScript conversion is the process of analyzing a JSON data structure and generating TypeScript interface definitions that describe its shape. TypeScript interfaces provide compile-time type safety — they tell the TypeScript compiler (and your editor’s IntelliSense) exactly what properties an object has, what types those properties are, and whether they are required or optional. Writing these interfaces by hand is tedious and error-prone, especially for large or deeply nested API responses.

This tool automates the process. It parses your JSON, infers the type of every value (string, number, boolean, null, array, or nested object), and generates clean TypeScript interfaces that you can drop straight into your codebase. Nested objects are extracted into separate named interfaces for readability. If you are working with JSON APIs, this tool pairs well with the JSON Formatter for inspecting the raw response and JSON Schema Generator for creating validation schemas alongside your types.

Examples

1. API response to TypeScript interface

Given this API response JSON:

{
  "id": 42,
  "name": "Alice Johnson",
  "email": "alice@example.com",
  "isActive": true,
  "address": {
    "street": "123 Main St",
    "city": "Springfield",
    "zipCode": "62701"
  },
  "roles": ["admin", "editor"]
}

The generator produces:

interface User {
  id: number;
  name: string;
  email: string;
  isActive: boolean;
  address: UserAddress;
  roles: string[];
}

interface UserAddress {
  street: string;
  city: string;
  zipCode: string;
}

2. Nested configuration object to types

Application config objects often have deep nesting:

{
  "database": {
    "host": "localhost",
    "port": 5432,
    "credentials": {
      "username": "app_user",
      "password": "secret"
    }
  },
  "cache": {
    "enabled": true,
    "ttlSeconds": 3600
  },
  "features": ["search", "export", "notifications"]
}

Each nested object becomes its own interface: ConfigDatabase, ConfigDatabaseCredentials, and ConfigCache. This keeps the types modular and reusable.

3. Array of objects to typed array

When your JSON is an array of objects (common in list endpoints):

[
  { "id": 1, "title": "Fix login bug", "status": "done", "priority": 1 },
  { "id": 2, "title": "Add search", "status": "in_progress", "priority": 2 },
  { "id": 3, "title": "Update docs", "status": "todo", "priority": 3 }
]

The generator creates an interface for the array item type. You can then use it as Task[] in your code to get full type safety when iterating, filtering, and mapping over the list.

Common Use Cases

Typing API responses: Generate interfaces from a real API response to get immediate type safety for fetch calls, Axios requests, or tRPC endpoints.
Configuration objects: Create types for config.json or environment-based settings so that typos and missing fields are caught at compile time.
Database record types: Paste a sample database row (as JSON) to generate the TypeScript type for your ORM models or repository layer.
Test fixture typing: Type your JSON test fixtures so that test files get IntelliSense and catch schema drift automatically.
SDK development: When building a TypeScript SDK for an API, generate initial interfaces from example responses, then refine them with optional fields and union types.
Migration from JavaScript: When converting a JavaScript project to TypeScript, generate interfaces from runtime JSON to quickly type existing data structures.
Documentation: Include generated interfaces in API documentation to show consumers the exact shape of response objects.

Frequently Asked Questions

Does it generate interfaces or type aliases?

The tool generates TypeScript interfaces by default. Interfaces are the standard choice for defining object shapes in TypeScript because they support declaration merging, produce more readable error messages, and are the convention used by most TypeScript projects.

Can it handle deeply nested objects?

Yes. Each nested object is extracted into its own named interface, and the parent interface references it by name. This keeps the output clean and avoids deeply indented inline type definitions. Array items are also typed — if an array contains objects, a separate interface is generated for the item type.

What about optional fields?

The generator infers types from a single JSON example, so all fields present in the input are treated as required. If you need optional fields, add a ? to the property name in the generated interface. For more accurate optional detection, provide a JSON array with multiple objects — fields missing from some objects can then be identified as optional.

Does it support enums?

The generator does not produce TypeScript enums automatically, since JSON values do not carry enough information to distinguish an enum from a regular string or number. If you know a field has a fixed set of values, replace the inferred string type with a union type like "active" | "inactive" after generating.

How does it handle arrays?

Arrays are typed based on their contents. An array of strings becomes string[], an array of numbers becomes number[], and an array of objects generates a separate interface for the item type. Mixed-type arrays produce a union type like (string | number)[].

Can I customize the root interface name?

Yes. Use the “Root interface” input field above the editor to set a custom name for the top-level interface. This name is also used as a prefix for nested interfaces.

Is my data sent to a server?

No. All type generation happens entirely in your browser using JavaScript. Your JSON data never leaves your machine.

Privacy & How It Works

The JSON to TypeScript generator runs entirely in your browser. When you click Generate, the tool parses your JSON and walks the data structure to infer types, then produces TypeScript interface definitions — all using JavaScript running locally in your browser tab. No data is transmitted to any server, no cookies track your usage, and nothing is stored after you close the tab. This makes it safe to generate types from production API responses, internal configuration files, and customer data. You can verify this by opening your browser’s Network tab. Other tools on JsonDevKit, including the JSON to Zod generator, JSON to Pydantic converter, and JSON Formatter, work the same way.

JSON to TypeScript Interface Generator