What is a JSON to TypeScript Converter?
Turn a sample JSON response into TypeScript interfaces you can paste straight into your project, with types inferred from the actual values in your data.
A JSON to TypeScript converter reads the shape of a JSON document and emits matching interface definitions, which saves you from hand-writing types every time an API response changes.
This converter handles nested structures, custom root interface names, and modern TypeScript syntax, so the output fits into any codebase that already uses strict typing.
How to Use Our JSON to TypeScript Converter
- Paste your JSON data into the left editor or click the sample data button to load example JSON
- Enter your desired root interface name in the interface name input field
- The tool validates your JSON and highlights any syntax errors immediately
- The converter generates TypeScript interfaces with proper type annotations in real-time
- Nested JSON objects are automatically converted into separate TypeScript interfaces
- Copy the generated TypeScript code to clipboard or download it as a .ts file
Examples
The converter inspects the JSON values, infers a TypeScript type for each field, and emits one interface per distinct object shape.
Example 1: Flat user object with primitive fields
Strings, numbers, and booleans map one-to-one with their TypeScript counterparts, so a simple JSON document lands as a single interface.
Input
{
"id": 42,
"name": "Alice",
"active": true
}Output
export interface User {
id: number;
name: string;
active: boolean;
}Example 2: Nested objects and nullable fields
A nested address object gets its own interface, and a field whose value is null widens to a union with null.
Input
{
"id": 1,
"name": "Alice",
"phone": null,
"address": {
"city": "Seoul",
"zip": "04524"
}
}Output
export interface User {
id: number;
name: string;
phone: string | null;
address: Address;
}
export interface Address {
city: string;
zip: string;
}JSON specification reference
Quick reference from RFC 8259. The converter enforces these rules on input; anything outside them is rejected or normalized.
| Element | Meaning | Example |
|---|
| Object | Unordered set of key/value pairs | {"a": 1} |
| Array | Ordered list of values | [1, 2, "x"] |
| String | Unicode, double-quoted only | "hello" |
| Number | IEEE 754 double, no NaN / Infinity | 3.14 |
| Literal | true / false / null only | null |
Common invalid forms
{'a': 1} // single quotes not allowed
{a: 1} // unquoted keys
{"a": 1,} // trailing comma
NaN // not permitted by RFC 8259Key Features
- Interface Generation: Creates TypeScript interfaces with proper type annotations, providing compile-time safety and IDE autocompletion
- Smart Type Inference: Automatically maps JSON values to TypeScript types — string, number, boolean, null, arrays, and nested objects
- Nested Interface Support: Nested JSON objects generate separate TypeScript interfaces with proper references between them
- Nullable Type Handling: Null values are correctly typed as union types (e.g.,
string | null) for accurate type safety - 100% Client-Side: All code generation happens in your browser — your data never leaves your device, ensuring complete privacy
Frequently Asked Questions
Q: How does the converter handle JSON arrays with mixed element types?
When a JSON array contains elements of different types (e.g., strings and numbers), the converter generates a TypeScript union type such as (string | number)[]. For arrays of objects with varying shapes, it merges all unique keys into a single interface with optional properties, giving you maximum type coverage while keeping the interfaces practical to use.
Q: Does the converter generate interfaces or type aliases?
The converter generates TypeScript interfaces by default, which is the recommended approach for defining object shapes in TypeScript. Interfaces provide excellent IDE support with autocompletion and compile-time type checking for your JSON data structures.
Q: How are optional and nullable fields handled?
The converter analyzes JSON values to determine appropriate TypeScript types. Null values are typed as nullunion types, and fields that may be absent can be marked as optional. This produces type-safe interfaces that accurately reflect your JSON data's structure.
Q: Are there any file size limitations?
There is no hard file size limit. Since all processing happens in your browser, the practical limit depends on your device's available memory. Most modern browsers can handle JSON files up to several megabytes without issues.
Q: Can I use the generated interfaces with React, Next.js, or Angular?
Yes. The generated TypeScript interfaces are framework-agnostic and work with React, Next.js, Angular, Vue, and any other TypeScript-based project. Simply import the interfaces to add type safety to your API calls and data handling.