JSON to TypeScript Converter — Free, No Signup

How to use

1. Paste JSON — Paste any JSON object, array, or value into the input.
2. Set Root Name — Name the top-level interface (e.g. User, ApiResponse).
3. Copy Types — Copy the generated TypeScript interfaces into your project.

Free JSON to TypeScript Converter

This tool turns any JSON sample into ready-to-use TypeScript interfaces or type aliases. Paste an API response, GraphQL payload, or config blob and instantly get strongly typed definitions you can drop into your codebase. No signup, no upload — everything runs locally in your browser.

How JSON to TypeScript Inference Works

The converter walks your JSON tree and infers a type for every value: primitives become string, number, boolean, or null; arrays are inferred from the union of their elements; and objects become named interfaces. Property keys that aren't valid identifiers are quoted automatically so the output always compiles.

Interfaces vs Type Aliases

Use interfaces when you want declaration merging or when modeling object shapes that other code can extend. Use type aliases when you need unions, intersections, or mapped types. The toggle lets you switch instantly without re-parsing your JSON.

Common Use Cases

• API integration: Generate response types from a real backend payload in seconds.
• Migrating JS → TS: Bootstrap interfaces for legacy JSON fixtures and config files.
• Mock data: Type your test fixtures so refactors don't silently break tests.
• GraphQL & REST docs: Convert example payloads in documentation into copy-pasteable types.

Privacy

All inference runs in your browser. Your JSON never reaches our servers, which makes the tool safe for sensitive payloads and proprietary schemas.

Need related tools? Try the JSON Formatter, JSON Validator, or YAML ↔ JSON Converter.

Frequently asked questions

Does it handle nested objects and arrays?

Yes. Each nested object becomes its own interface, and array element types are inferred by merging all items.

Interface vs type alias — which should I use?

Toggle between them. Interfaces are open for declaration merging; type aliases support unions/intersections better.

How are mixed-type arrays handled?

Element types are merged. If types conflict, the element falls back to any so your code still compiles.

Are null values supported?

Yes. null produces the literal null type. You can manually widen to nullable unions if needed.

Is my JSON sent anywhere?

No. Conversion is processed locally in your browser using a pure-JS inference algorithm.

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