Null Values & Optional Fields – JSON to Typedef Example
Demonstrate how null values in JSON are converted to optional fields in TypeScript (?) and nullable types in C# (?). Essential for API response typing.
What this demonstrates: This example has many null fields at different levels. In TypeScript, each null field becomes optional (?) with type | null. In C#, value types like bool become bool? while string remains as-is. This pattern is common in API responses where fields may not be populated.
Paste JSON on the left to generate typedefs
Supports Nested Objects and Arrays
Our converter recursively processes deeply nested JSON structures, including arrays of objects, mixed-type arrays, and multi-level object hierarchies. Each nested object gets its own named interface (TypeScript) or class (C#) with properly typed properties.
Optional Fields and Mixed Types Handled
When a field is null in your JSON, it's automatically marked as optional in TypeScript (with ?) or nullable in C#. Arrays with mixed element types produce union types or fallback to object.
How to Use This JSON to Typedef Converter
Paste JSON
Paste or type your JSON into the input area on the left.
Choose Language
Select TypeScript or C# from the dropdown.
Copy Output
Your type definitions appear instantly. Click Copy to use them.