How are null values and optional properties handled?

A field is optional (?) when it is missing from some array items, and null values are kept as | null (e.g. avatarUrl?: string | null).

Can I choose between TypeScript 'interface' and 'type' keywords?

Yes. You can toggle between exporting 'interface' definitions or 'type' aliases based on your project's ESLint and coding standards.

Is my proprietary JSON API data sent over the network?

No. The conversion runs locally in your browser. Your JSON is only sent to our AI provider if you click "Add JSDoc comments (AI)".

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AI Tools

Smart JSON to TypeScript Converter

Convert JSON to TypeScript interfaces instantly in your browser. Keeps your exact key names, infers optional fields, unions and nulls from the data, with optional AI JSDoc comments.

Instant ResultsNo Sign-up Required100% Free Utility

JSON Input

Types are generated live in your browser. Property names are kept exactly as in your JSON; a key is optional (?) only when it is missing from some array items.

Root type name

Declare as

Add export

Readonly properties

How to Use This Tool

Paste your JSON: any valid JSON object or array, including nested objects and arrays of objects.
Pick options: root type name, interface or type, export and readonly.
Copy or download: the TypeScript updates as you type. Copy it or download it as a .ts file.
Optional AI comments: click "Add JSDoc comments (AI)" to get a short description above each field.

Key Features

Exact Key Names

Property names stay exactly as in your JSON (user_id stays user_id), so the types match the data you receive.

Optional Fields From Real Data

A field is marked optional only when some array items don't have it. Nothing is guessed.

Unions and Nulls

Mixed values become union types and null values are kept, instead of being silently dropped.

AI JSDoc Comments (optional)

AI writes short field descriptions on request. Your types are generated locally and never changed by the AI.

About Smart JSON to TypeScript Converter

Convert raw JSON objects and API response payloads into clean, type-safe TypeScript interfaces and type aliases. Supports nested objects, arrays, union types, optional fields, and JSDoc annotations.

Why Choose Our JSON to TypeScript Converter

Feature	Smart Toolverse	Others
Smart Type Inference	Accurately detects string, number, boolean, null, unions & arrays	Falls back to 'any' for complex types
Nested Interface Extraction	Generates clean modular sub-interfaces for nested objects	Generates massive single inline objects
Type vs Interface Toggle	Switch between 'type' aliases and 'interface' declarations with 1 click	Interface only
Client-Side Execution	Converts JSON locally in your browser (AI comments are optional)	Sends proprietary API payloads to remote servers

Common Uses & Applications

Quickly generate TypeScript type definitions from REST and GraphQL API responses, accelerate frontend React/Next.js development, and prevent runtime type bugs with full static typing.

Frequently Asked Questions

The converter recursively traverses nested objects, creating distinct, cleanly named TypeScript interfaces (e.g. User, Address, OrderItem) and referencing them within parent structures.