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What is JSON to TypeScript?

Free JSON to TypeScript converter. Paste any JSON object and get TypeScript interfaces generated instantly. Handles nested objects, arrays, optional fields, and null types. No signup required.

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JSON to TypeScript runs entirely in your browser using JavaScript (browser). Your data never leaves your device.

Free JSON to TypeScript

Paste any JSON and get production-ready TypeScript interfaces in seconds. The generator handles deeply nested objects, arrays of objects, mixed arrays, null values (as optional fields), and primitive types. Choose between interface and type alias output. Control the root interface name. Copy the output with one click and paste directly into your TypeScript project.

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Frequently Asked Questions

Any valid JSON: nested objects, arrays of primitives, arrays of objects, mixed arrays, null values, booleans, numbers, and strings. Deeply nested structures are handled recursively.
Null values are typed as the field being optional (e.g., `field?: string | null`). This reflects real-world API responses where a field can be absent or null.
Arrays of a single type become `type[]` (e.g., `string[]`, `number[]`). Arrays of objects generate a nested interface. Mixed-type arrays use a union type (e.g., `(string | number)[]`).
Both are equivalent for most use cases. Use `interface` when you want to extend or merge declarations (common in larger codebases). Use `type` for union types or when the structure won't be extended. Interfaces are generally preferred for object shapes by TypeScript style guides.
Yes. The output follows TypeScript syntax and can be pasted directly into a .ts or .d.ts file. Field names that are not valid TypeScript identifiers are automatically quoted.

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Why Generate TypeScript Interfaces from JSON?

Modern TypeScript projects rely on strong typing of API responses to catch mismatches at compile time rather than at runtime. When a REST API returns JSON, manually writing TypeScript interfaces is tedious and error-prone — especially for large or deeply-nested payloads. Generating interfaces from a real API response gives you an accurate starting point in seconds. The generated types can then be refined (adding documentation comments, narrowing union types, or marking optional fields) before committing to source control.

interface vs type — When to Use Each

TypeScript interface and type are largely interchangeable for object shapes, but they have important differences. Interfaces support declaration merging (two interface Foo declarations in the same scope are merged), which is useful in some library-authoring scenarios. Type aliases (type) support union types, intersection types, and conditional types — capabilities that interfaces lack. For API response types that you control and won't extend externally, either works. The TypeScript team's official style guide slightly favors interface for object shapes and type for unions and utility types.

Handling Null Fields

A JSON field that is null in one API response may be a string in another. This tool marks null-valued fields as field?: TypeHere | null, making them optional to reflect that the API may omit them. After generating the interface, audit null fields against the API documentation to determine whether the real type is string | null, number | null, or something else. Replacing null with the correct type prevents the most common class of TypeScript "possibly null" errors in production code.