No. Parsing and inference happen in your browser. Nothing is transmitted or stored.

Why is a field typed `null` instead of `string | null`?

Because in the sample provided it was only ever null, and there is nothing else to infer from. Widen it by hand, or paste a sample where the field carries a value.

Why is everything required?

One example cannot distinguish 'always present' from 'present this time'. Adding ? where appropriate is the manual step this tool deliberately leaves to you.

JSON to TypeScript

Runs in your browser

Generate TypeScript interfaces from a JSON sample, with nested objects turned into their own named types. Runs in your browser.

JSON

Root interface name

About this tool

Typing an API response by hand is tedious and error-prone, especially when it nests several levels deep. Feeding in one real response gets you most of the way in a second. Treat the output as a first draft rather than a contract: inference can only describe the sample it was given, so a field that happens to be null in your example, or an array that happens to be empty, cannot reveal its real type — and nothing in a single sample distinguishes an optional field from a required one.

How to use

Paste a representative JSON response — ideally one with all optional fields populated.
Name the root interface.
Copy the generated interfaces and adjust optionality and nullability by hand.

When to use this tool

Typing a third-party API response you have no schema for.
Bootstrapping DTOs from a sample payload.
Turning a fixture file into types for a test.
Documenting the shape of a legacy endpoint.

Tips

Pick a sample where every optional field is present, otherwise those fields will be missing from the output entirely.
Mark fields optional with ? yourself — a single sample cannot tell the generator which are.
If a field can be null as well as a value, widen it to `string | null` manually.

Limitations

Types are inferred from a single sample. A field that is null or an empty array in your example cannot reveal its real type, and optional fields look required.

FAQ

Is my JSON uploaded?: No. Parsing and inference happen in your browser. Nothing is transmitted or stored.
Why is a field typed `null` instead of `string | null`?: Because in the sample provided it was only ever null, and there is nothing else to infer from. Widen it by hand, or paste a sample where the field carries a value.
Why is everything required?: One example cannot distinguish 'always present' from 'present this time'. Adding ? where appropriate is the manual step this tool deliberately leaves to you.