How are JSON arrays handled in TypeScript?

JSON arrays are typed based on their contents. An array of strings becomes string[], an array of numbers becomes number[], and an array of objects becomes a named interface array like User[]. Mixed-type arrays become union types.

JSON to TypeScript Converter

Generate TypeScript interfaces and types from JSON data instantly. Handles nested objects, arrays, union types, and optional properties.

100% client-side. Your data never leaves your browser.

Root Interface Name

Output Style

Indent

Export keyword All properties optional Readonly properties Trailing semicolons

JSON Input Upload .json

TypeScript Output

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Smart Naming

Nested objects get PascalCase interface names derived from their property keys. Arrays of objects generate clean, reusable types.

Union Types

Mixed arrays like [1, "hello", true] become (number | string | boolean)[]. Null values produce union types with null.

Configurable Output

Choose interface vs type, export keyword, optional/readonly modifiers, semicolons, and indentation to match your project's code style.

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Frequently Asked Questions

How do I convert JSON to TypeScript interfaces?

Paste your JSON data or upload a .json file. The tool analyzes the structure and generates TypeScript interfaces with properly typed properties. Nested objects become separate interfaces for clean, reusable code.

Should I use interface or type in TypeScript?

Interfaces are preferred for defining object shapes because they support declaration merging and extends. Type aliases are better for unions, intersections, and complex mapped types. For API response typing, interfaces are the standard choice.

How are JSON arrays handled?

Arrays of primitives become typed arrays (string[], number[]). Arrays of objects are merged into a single interface representing all possible properties. Mixed arrays become union types like (string | number)[].

Does it handle nested JSON objects?

Yes! Each nested object is extracted into its own named interface. For example, a user with an address field generates separate User and Address interfaces, keeping your code modular and reusable.

Can I make all properties optional?

Yes! Check "All properties optional" to add the ? modifier to every property. This is useful for Partial<T> patterns, form state types, or API payloads where fields are conditionally present.