JSON to TypeScript/C#Typedef Converter
Paste your JSON and instantly generate clean, production-ready TypeScript interfaces or C# classes. Handles deeply nested objects, arrays, mixed types, and optional fields — all client-side, no data leaves your browser.
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.
Why Use Our JSON to Typedef Converter?
Working with APIs and JSON data is a daily task for modern developers. Manually writing TypeScript interfaces or C# classes from JSON responses is tedious and error-prone. Our converter automates this process, saving you time and reducing bugs.
Key Features
- Instant Conversion — Type definitions generate automatically as you type, with a 500ms debounce for smooth performance.
- Deep Nesting Support — Recursively processes objects nested at any depth, creating separate named types for each level.
- Array Intelligence — Infers element types from array contents, handling mixed-type arrays with union types (TS) or object fallback (C#).
- Null Safety — Null values automatically create optional fields in TypeScript and nullable types in C#.
- Privacy First — Everything runs in your browser. Your JSON data never leaves your machine.
- Syntax Highlighting — Output is displayed with full syntax highlighting for easy reading and code review.
Common Use Cases
- Converting REST API JSON responses into TypeScript interfaces for frontend development.
- Generating C# model classes from JSON payloads for .NET backend services.
- Creating type definitions for configuration files, database exports, or third-party API schemas.
- Rapidly prototyping data models from sample JSON during hackathons or sprint planning.
Frequently Asked Questions
Is my JSON data safe?
Yes. The converter runs entirely in your browser using client-side JavaScript. No data is sent to any server.
What JSON structures are supported?
All valid JSON is supported: objects, arrays, nested objects, arrays of objects, mixed types, null values, strings, numbers, and booleans at any depth.
How are null values handled?
In TypeScript, null fields are marked with ? and typed as type | null. In C#, value types become nullable (e.g., int?).
Can I customize the root type name?
Yes. Use the "Root Type Name" input to set any valid identifier as the top-level interface or class name.
Learn Guides
Deep-dive into TypeScript interfaces, C# classes, JSON data types, edge cases, and real-world API typing patterns.
Try These Examples
Pre-loaded JSON examples demonstrating different conversion scenarios. Click to open the converter with the example loaded.