How It Works
This tool parses your JSON input and recursively generates TypeScript interface definitions. Each nested object becomes its own named interface using PascalCase derived from the property key. Arrays are analyzed to determine the element type — if the array contains objects, their fields are merged to produce a single comprehensive interface.
The conversion runs entirely in your browser. No data is sent to any server, making it safe for proprietary API responses and sensitive payloads.
Why Convert JSON to TypeScript?
Working with untyped API responses is the #1 source of runtime errors in TypeScript projects. By converting a sample response into an interface definition, you get:
- Autocomplete — your editor knows every field and its type.
- Compile-time safety — catch misspelled keys and wrong types before your code runs.
- Self-documenting code — interfaces act as living documentation of your data shapes.
- Refactoring confidence — change a type and TypeScript flags every affected file.
Supported Features
| Feature | Example Input | Generated Output |
|---|---|---|
| Primitive types | "name": "Alice" | name: string |
| Numbers | "age": 30 | age: number |
| Booleans | "active": true | active: boolean |
| Nullable fields | "bio": null | bio: unknown | null |
| Nested objects | "address": { "city": "NY" } | address: Address (separate interface) |
| String arrays | "tags": ["a", "b"] | tags: string[] |
| Object arrays | "users": [{ "id": 1 }] | users: User[] (separate interface) |
FAQ
Is my data safe?
Yes. The entire conversion happens client-side in your browser using JavaScript. Your JSON is never transmitted to a server. You can verify this by opening your browser's Network tab — no requests are made when you paste or convert.
Can I convert deeply nested JSON?
Yes. The tool recursively traverses your JSON structure to any depth. Each nested object generates its own interface, keeping the output clean and modular.
What about arrays with mixed types?
If an array contains multiple primitive types (e.g., numbers and strings), the tool generates a union type like (string | number)[]. For arrays of objects, fields from all objects are merged into a single interface.
Does it handle optional properties?
Fields with a null value are typed as type | null. When processing arrays of objects, if a field appears as null in some items but has a value in others, it is correctly marked as nullable.
Can I use the output in my project directly?
Absolutely. Click the Copy button and paste the interfaces into your .ts or .d.ts file. The generated code uses standard TypeScript syntax with no dependencies.