How does the converter know if a field is optional?

It infers types from the single sample you paste, so it can't know a field is sometimes absent unless your sample shows it. Provide a complete example, then add the ? optional marker by hand for fields the API may omit.

What happens with null values in my JSON?

A null produces a null type for that field. If a field is sometimes a value and sometimes null, widen it to a union like string | null yourself, since one sample can't reveal both cases.

Does it generate interfaces or type aliases?

It produces TypeScript type definitions mirroring your JSON's nested structure. Use whichever style fits your codebase; the two are largely interchangeable for describing data shapes.

Can I paste a JSON array instead of an object?

Yes. The converter inspects array elements and generates the element type, so you can paste an array of records and get a type for the items.

Is my JSON sent anywhere?

No. Conversion happens locally in your browser, so it's safe to paste real API responses containing sensitive data.

JSON to TypeScript Converter

Instantly convert JSON objects or arrays into clean TypeScript interfaces or type aliases. Paste your JSON data below.

Options

Configure TypeScript generation settings

Root Type/Interface Name

Output Type

Use interfaces

Generates interface declarations

Key Normalization

Keep original keys

Preserves original key format

JSON Input

Paste your JSON object or array here

TypeScript Output

Generated interfaces

About JSON to TypeScript Converter

When you consume an API that has no published types, the fastest way to get type safety is to take a real response and turn it into a TypeScript interface. Doing that by hand means reading every field, guessing whether a value is a string or a number, spotting nested objects, and remembering to mark things optional — slow, and easy to get subtly wrong.

This converter does it instantly. Paste a JSON object or array and it infers the shape: primitive types per field, nested interfaces for nested objects, array element types, and unions where values differ. You get clean, ready-to-paste TypeScript you can drop straight into your codebase and refine, instead of typing it out structure by structure.

It runs entirely in your browser, so you can paste production API responses — including ones with real customer data — without anything being uploaded. Generate the types, copy them out, then clear the input.

How to use JSON to TypeScript Converter

Paste a JSON sample
Use a representative response — ideally one with all optional fields populated — so the inferred types cover every property the API can return.
Review the generated types
The tool produces TypeScript interfaces (or type aliases) mirroring the JSON structure, with nested objects broken into their own named types.
Adjust for edge cases
Inference works from one sample, so widen types by hand where a field can be null, optional, or a union the sample didn't show.
Copy into your project
Paste the result into a .ts file. Rename the root interface to something meaningful for your domain.

Frequently asked questions

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