JSON to TypeScript Interface Generator | Instant Type Definitions

The JSON to TypeScript Interface Generator automatically creates TypeScript type definitions (Interface or Type Alias) by simply pasting your JSON data.

Nested objects are automatically extracted as separate interfaces. When objects within arrays have different keys, those keys are properly inferred as optional properties (?). Real-time conversion means results appear instantly as you type.

No JSON data is ever sent to a server. Safely convert sensitive API response data into type definitions. Free to use, no registration required.

Interface

A TypeScript syntax for defining object shapes. Written as interface User { name: string; }. Supports declaration merging.

Type Alias

An alternative to interfaces using the type keyword. More versatile — supports union types and mapped types.

Union Type

A type that can be one of several types. Expressed using |, e.g., string | number.

Optional Property (?)

Adding ? after a property name indicates it may be undefined.

Readonly

A modifier that makes a property read-only. readonly name: string prevents reassignment.

This tool performs type inference using vanilla JavaScript only, with no external library dependencies.

Recursive Type Inference

Data parsed via JSON.parse() is recursively traversed. Each value's JavaScript type (typeof/Array.isArray) is mapped to its TypeScript equivalent. Nested objects are automatically extracted as separate interfaces.

Optional Property Inference

When an array contains multiple objects, the tool compares key sets across all objects. Keys present in all objects become required properties; keys in only some objects become optional (?).

Q. Is any data sent to a server?

A. No. All JSON parsing is performed entirely in your browser. No data is ever transmitted.

Q. Does it work on mobile?

A. Yes. Fully responsive and works on smartphones and tablets.

Q. Can it handle JSON with non-ASCII keys?

A. Yes. Non-standard keys are properly output as quoted properties.

Q. Should I use interface or type?

A. It depends on your project conventions. Generally, interface is preferred. Use type when you need union types or mapped types.

Q. Does it handle deeply nested JSON?

A. Yes. Recursive analysis means there's no depth limit.

Q. What if array objects have different keys?

A. Common keys become required; keys only in some objects become optional (?).

Q. Is this tool free?

A. Yes. Completely free with no usage limits.

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