What is JSON to TypeScript with Optional Fields Generator?
This tool converts JSON data into TypeScript interface definitions with support for optional fields (?), readonly modifiers, and nested type inference. It automatically determines field types from JSON values and can mark fields as optional based on null values or user preferences.
How to Use
- Configure options: mark null fields as optional, mark all fields as optional, or add readonly modifiers
- Paste your JSON data into the input area
- Click "Generate" and copy the TypeScript interfaces into your project
Why Use This Tool?
Tips & Best Practices
- Use realistic sample data — type inference depends on actual values
- Enable "Mark null fields as optional" to handle nullable API responses
- Use readonly modifier for immutable data structures and better type safety
- Nested objects become separate interfaces with PascalCase names
Frequently Asked Questions
How are JSON types mapped to TypeScript?
JSON strings → string, numbers → number, booleans → boolean, null → optional field or null type, arrays → T[], objects → separate interface definitions.
What does the optional field marker (?) do?
The ? modifier in TypeScript indicates that a field may be undefined. This is useful for API responses where certain fields may not always be present.
What is the readonly modifier for?
The readonly modifier prevents reassignment of properties, making your data structures immutable. This is useful for state management and preventing accidental mutations.
How are nested objects handled?
Nested JSON objects are converted to separate TypeScript interfaces with their own definitions. They are ordered children-first so that referenced types are defined before they are used.
Is my data sent to a server?
No, all processing happens entirely in your browser. Your JSON data never leaves your device.