JSON to TypeScript

What is JSON to TypeScript?

JSON to TypeScript is a developer tool that automatically generates TypeScript interface or type declarations from raw JSON data. When working with REST APIs, configuration files, or any JSON data source, manually writing TypeScript types is tedious and error-prone. This tool analyzes the structure of your JSON — including nested objects, arrays, mixed-type arrays, and null values — and produces clean, accurate TypeScript definitions you can drop directly into your codebase.

How to Use This Tool

1. Paste or type your JSON data into the JSON Input panel on the left.
2. Set a Root name for the top-level interface (defaults to “Root”).
3. Choose whether to generate interface or type declarations using the checkbox.
4. Toggle Export keyword on or off depending on whether you need exported types.
5. Enable Optional properties if you want every property marked with ?.
6. Click Generate to produce the TypeScript output on the right.
7. Use Copy or Download to export the generated types.

Key Features

• Nested object support — deeply nested JSON objects become separate named interfaces with proper references.
• Array type inference — arrays of objects are merged to detect all possible keys, with optional markers for fields not present in every element.
• Mixed-type arrays — arrays containing different primitive types produce union types like (string | number)[].
• Null handling — null values are typed as null so you can add proper null checks.
• Safe key names — keys with special characters are automatically quoted.
• Duplicate detection — interfaces with identical shapes are reused, while name collisions are resolved with numeric suffixes.

When to Use This Tool

Use this tool when bootstrapping type-safe API response types, generating interfaces from API documentation or sample payloads, migrating JavaScript projects to TypeScript, or creating type definitions for configuration files. It is also useful for learning how TypeScript types map to JSON structures.

Tips and Best Practices

• Provide a representative sample with all possible fields populated for the most accurate types.
• Use arrays with multiple objects so the tool can detect optional fields automatically.
• Choose type over interface when you need union types or mapped types downstream.
• Review generated types and add JSDoc comments for documentation.
• All processing happens entirely in your browser — your data never leaves your device.