JSON to TypeScript

Convert JSON objects into TypeScript interfaces with automatic type inference, nested object support, and array detection.

JSON to TypeScript

Convert JSON objects into TypeScript interfaces instantly

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Nested objects and arrays are converted into separate interfaces. In arrays of objects the shapes are merged: a key missing from some items becomes optional, and differing value types become a union.

Paste JSON above and click "Convert" to generate TypeScript interfaces

What is a JSON to TypeScript Converter?

A JSON to TypeScript converter is a tool that takes a JSON object or array and automatically generates TypeScript interface definitions that match the data structure. TypeScript interfaces provide type safety and autocompletion in your IDE, but writing them manually from API responses or JSON data is tedious and error-prone.

CodeHelper's JSON to TypeScript Converter handles nested objects (creating separate interfaces), arrays (with item type inference), union types for mixed arrays, and null values: all in a single click.

Key Features

  • Automatic Type Inference: Detects string, number, boolean, null, object, and array types from your JSON data.
  • Nested Interfaces: Nested objects are extracted into their own named interfaces for clean, reusable code.
  • Array Detection: Arrays are typed based on their contents, including union types for mixed arrays.
  • Export Toggle: Add the export keyword to all generated interfaces.
  • Optional Properties: Mark all properties as optional with the ? modifier.

How to use the JSON to TypeScript Converter

  1. Paste your JSON data into the input area.
  2. Set the root interface name (defaults to "Root").
  3. Toggle export and optional properties as needed.
  4. Click Convert to generate TypeScript interfaces.
  5. Copy the output or download it as a .ts file.

Whether you are consuming REST APIs, working with configuration files, or bootstrapping a new TypeScript project, this free tool generates accurate type definitions from any JSON structure in seconds.

Generating types for an API response? Browse the public API directory to find documented endpoints with sample JSON, from music to cryptocurrency data.

Frequently Asked Questions

How do I convert a JSON API response to TypeScript interfaces?

Paste the JSON, set a root interface name and click Convert. Objects become interfaces, nested objects become their own named interfaces, and arrays of objects are merged into one interface that describes every item. Copy the output or download it as a .ts file.

Why are some properties marked optional in the generated interface?

In an array of objects, a key that is present in some items and missing in others is inferred as optional, with the ? modifier. This mirrors how the data actually behaves and avoids runtime undefined values on properties that TypeScript would otherwise treat as always present.

How are null values typed?

A property that is null in some items and a string in others becomes string | null, and a property that is always null stays null. Nothing is silently widened to any, so the generated types remain strict.

What type does an empty array get?

An empty array is typed as unknown[], because its contents cannot be inferred. Replace unknown with the real item type once you know it, or paste a sample that contains at least one element.

Is my JSON uploaded to a server?

No. The conversion runs entirely in your browser with client side JavaScript. Nothing is sent, stored or logged, which makes the tool safe for API responses that contain private data.

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