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JSONからTypeScriptインターフェースジェネレーター

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入力

自動処理

出力

クライアント側

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ガイド

JSONからTypeScriptインターフェースジェネレーター

Instantly convert any JSON object or array into clean, ready-to-use TypeScript interfaces. Paste your JSON, configure your preferred export style, and get properly typed definitions with nested interfaces, optional fields, and union types — all generated client-side in real time.

使い方

Paste your JSON data into the input area. The tool instantly generates TypeScript interfaces in the output panel. Adjust the root interface name, export style (interface, type alias, or class), and null handling to match your project conventions.

特徴

Recursive Type Inference – Automatically detects strings, numbers, booleans, arrays, and nested objects, generating separate named interfaces for each level of nesting.
Optional Field Detection – When parsing arrays of objects, fields that don’t appear in every item are marked as optional with the ? modifier.
Union Types – Mixed-type arrays are correctly typed as unions (e.g., (string | number)[]).
Export Styles – Choose between interface, type alias, or class declarations to match your codebase conventions.
Configurable Null Handling – Choose whether null values map to | null または | undefined in the generated output.
Real-Time Generation – Output updates instantly as you type or modify options, with no manual button clicks required.

このツールを使用するタイミング

This tool is ideal when you’re integrating a REST API and need TypeScript types from sample responses, migrating a JavaScript project to TypeScript, or prototyping with JSON data and want type-safe access throughout your codebase. Instead of manually writing interfaces for deeply nested API responses, paste the JSON and get accurate types in seconds.

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 よくある質問

What is a TypeScript interface and why should I use one?

A TypeScript interface defines the shape of an object — its property names and their types. Interfaces enable compile-time type checking, autocomplete in editors, and better documentation of data structures. They catch bugs early by ensuring you access only properties that actually exist on an object.
What is the difference between interface and type alias in TypeScript?

Both define object shapes, but interfaces support declaration merging (extending an existing interface across files) and are traditionally used for object types. Type aliases are more flexible — they can represent unions, intersections, primitives, and tuples. For plain object shapes, either works; interfaces are the conventional choice for API response types.
How does TypeScript handle optional properties?

Optional properties are marked with a question mark (e.g., name?: string). This means the property may or may not exist on the object. TypeScript narrows the type to include undefined, so you must check for existence before using the value. This is useful for API responses where some fields are only present under certain conditions.
What is the difference between null and undefined in TypeScript?

Both represent absence of value, but they are distinct types. undefined means a variable has been declared but not assigned, while null is an intentional assignment of no value. In strict TypeScript, you must handle each explicitly. API responses typically use null for missing values, while optional object properties default to undefined.