JSON to TypeScript Interface Converter

Convert JSON to TypeScript interfaces instantly. Supports nested objects, arrays, and optional fields. Free, no upload, no signup.

JSON Input
1 lines · 0 chars
TypeScript Interface Output
Click Convert to see output here.

What is a JSON to TypeScript Converter?

A JSON to TypeScript converter is a developer tool that automatically generates TypeScript interface definitions from a JSON object. Instead of manually writing type definitions - which is time-consuming and error-prone - you simply paste your JSON and get ready-to-use TypeScript interfaces in seconds.

This tool also works in reverse - converting TypeScript interfaces into JSON Schema, which is a standard format used for API documentation, form validation, and runtime data validation with tools like Zod, Ajv, and Swagger.

JSON to TypeScript - How It Works

  • Primitive Types

    String values become string, numbers become number, booleans become boolean, and null values become optional fields marked with ?.

  • Nested Objects

    Nested JSON objects are automatically extracted into separate named interfaces. The parent interface references the child interface by name, keeping the code clean and reusable.

  • Arrays

    Arrays of strings become string[], arrays of numbers become number[], and arrays of objects generate a separate item interface with the Item[] syntax.

  • Date Detection

    String values that look like ISO date formats (e.g. 2024-01-15) are typed as string with a comment indicating they represent dates.

TypeScript to JSON Schema - How It Works

JSON Schema is a vocabulary that allows you to validate, document, and describe JSON data. Converting TypeScript interfaces to JSON Schema lets you reuse your type definitions across different tools and frameworks.

  • API Validation

    Use JSON Schema to validate incoming API request bodies and response data at runtime, catching errors before they cause bugs in production.

  • Swagger / OpenAPI

    JSON Schema is the foundation of OpenAPI documentation. Convert your TypeScript types to generate accurate API documentation automatically.

  • Form Validation

    Libraries like react-jsonschema-form use JSON Schema to automatically generate and validate forms from your type definitions.

  • Runtime Validation

    Use JSON Schema with validators like Ajv to validate data at runtime in JavaScript and TypeScript applications.

How to Convert JSON to TypeScript

  • Step 1: Select the JSON → TypeScript tab.
  • Step 2: Paste your JSON object into the input panel on the left. You can also click Sample to load an example.
  • Step 3: Optionally change the Root Name to match your type name (e.g. User, Product, ApiResponse).
  • Step 4: Click Convert to generate TypeScript interfaces.
  • Step 5: Click Copy to copy the output and paste it into your TypeScript project.

When Do Developers Use This Tool?

  • After getting a new API response and needing to type it for a React or Next.js project
  • When migrating a JavaScript project to TypeScript
  • When consuming third-party APIs and needing type-safe interfaces
  • When building forms and needing JSON Schema for validation
  • When writing Swagger or OpenAPI documentation
  • When adding runtime validation with Ajv or similar libraries
  • When setting up Zod schemas from existing data structures

Frequently Asked Questions

A JSON to TypeScript converter takes a JSON object and automatically generates TypeScript interfaces that match the structure and data types of that JSON. This saves developers from manually writing type definitions.

TypeScript interfaces provide type safety for your JSON data. When you define an interface, TypeScript will catch type errors at compile time — for example if you try to access a property that doesn't exist or use a string where a number is expected.

Nested objects in your JSON are automatically converted into separate TypeScript interfaces. For example, if your JSON has an 'address' object, the converter creates an 'Address' interface and references it from the parent interface.

JSON Schema is a standard format for describing the structure of JSON data. Converting TypeScript interfaces to JSON Schema lets you use the same type definitions for API validation, form validation, documentation tools like Swagger, and runtime data validation.

No. All conversion happens entirely in your browser using JavaScript. Your JSON and TypeScript code never leaves your device.

The Root Name field sets the name of the main TypeScript interface generated for your JSON object. The default is 'RootObject'. You can change it to match your actual type name, for example 'User', 'Product', or 'ApiResponse'.

Yes. Arrays of primitives like string[] or number[] are detected automatically. Arrays of objects create a separate interface for the item type and use the array syntax, for example Item[].

Yes. If a JSON field has a null value, it is marked as optional (with ?) in the TypeScript interface, since null values often indicate optional data.