What does the JSON to TypeScript Interface Generator do?

It converts a JSON object into TypeScript interface or type alias definitions. Paste in any valid JSON and the tool instantly generates strongly-typed TypeScript code, including separate named interfaces for nested objects and correct types for strings, numbers, booleans, nulls, and arrays.

What is the difference between interface and type in TypeScript?

Both interface and type can describe the shape of an object. Interfaces support declaration merging (you can extend the same interface in multiple places) and are generally preferred for public API contracts. Type aliases are more flexible — they can represent unions, intersections, and primitives. For plain object shapes like those generated from JSON, either works; the choice is mostly a style preference.

What does the 'Mark fields as optional' option do?

When enabled, every generated field gets a question mark (e.g. name?: string) to mark it as optional. This is useful when your JSON represents a partial response where some keys may be absent, such as a PATCH request body or a nullable API payload.

How does the tool handle nested objects?

Each nested JSON object generates a separate, named interface or type. The name is derived from the parent key using PascalCase (e.g. a key named 'address' produces an interface called Address). Nested interfaces are printed before the root interface so you can copy the entire output and it will compile without re-ordering.

How are arrays handled when elements have different types?

If all elements in an array share the same type (e.g. all strings), the output is string[] or Array . If elements have multiple distinct types, the tool generates a union type like (string | number)[]. Empty arrays use unknown[] since no element type can be inferred.

JSON to TypeScript インターフェース生成ツール

JSONオブジェクトをTypeScriptのinterfaceまたはtype aliasに即座に変換します。ネストされたオブジェクト、配列、null、混合型をすべて処理します。

ルート名

キーワード

配列構文

フィールドをoptionalにする

JSON入力

TypeScript出力

使い方

JSONオブジェクトをTypeScriptのinterfaceまたはtype aliasに即座に変換します。ネストされたオブジェクト、配列、null、混合型をすべて処理します。

1Paste your JSON object into the left panel, or click 'Load Sample' to try a pre-built example.
2Set the root interface name (default: Root), choose interface vs type, and adjust array syntax and optional field options.
3The right panel instantly shows the generated TypeScript interfaces as you type.
4Click 'Copy' to copy the complete TypeScript output to your clipboard.

主な機能

Generates separate named interfaces for all nested objects
Toggle between interface and type alias output
Choose T[] or Array<T> array syntax
Mark all fields as optional with a single toggle
Handles strings, numbers, booleans, null, arrays, and mixed-type unions
Real-time generation — no button clicks needed
100% browser-based, your JSON never leaves your device

JSON to TypeScript インターフェース生成ツール

使い方

主な機能

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