JSON to TypedefFrequently Asked Questions

It's a free, client-side tool that instantly converts JSON data into clean TypeScript interfaces or C# classes. Paste your JSON, choose your target language, and get production-ready type definitions in real time — no server calls, no sign-up required.

Visit the JSON to Typedef Converter page. Paste your JSON into the left panel, select TypeScript or C# from the dropdown, optionally set a custom root type name, and your type definitions appear instantly on the right. Click "Copy" to copy the output.

No. The converter runs entirely in your browser. There's nothing to install, no CLI tools, no packages. Just open the page and start converting.

Yes, 100% free. The tool is supported by advertising (Google AdSense) to help cover hosting costs and keep it available for everyone.

All valid JSON is supported: simple objects, deeply nested objects, arrays of primitives, arrays of objects, mixed-type arrays, null values, strings, numbers, booleans, and any combination at any depth level.

Each nested object automatically gets its own named interface (TypeScript) or class (C#). Names are derived from the JSON key in PascalCase. For example, a key called "shipping_address" produces an interface called ShippingAddress.

The converter inspects all elements in an array to infer the element type. Homogeneous arrays like [1, 2, 3] produce number[] in TypeScript or List<int> in C#. Arrays of objects produce typed arrays with a dedicated interface/class. Mixed-type arrays produce union types in TypeScript or List<object> in C#.

Null values are handled intelligently. In TypeScript, fields with null values are marked as optional (?) and typed as type | null. In C#, value types become nullable (e.g., int?) while reference types remain as-is.

Yes. Output code is fully syntax-highlighted using language-aware highlighting for both TypeScript and C#, making it easy to read and review before copying.

Absolutely. Use the "Root Type Name" input to set any valid identifier (e.g., ApiResponse, UserProfile, OrderData) as the top-level interface or class name. Defaults to RootObject.

The generated interfaces use standard TypeScript syntax compatible with TypeScript 3.x and above. No advanced features like template literal types or conditional types are used, so the output works everywhere.

Yes. All generated interfaces use the "export" keyword, so you can import them directly into your TypeScript files without modification.

Keys that are valid JavaScript identifiers are used as-is. Keys with special characters (spaces, hyphens, etc.) are wrapped in quotes. For example: "first-name"?: string;

When a JSON field is null, the converter marks it as both optional (?) and includes | null in the type. This means the field can be absent OR explicitly null, which is the safest pattern for TypeScript consumers.

The output uses standard auto-properties ({ get; set; }) compatible with C# 3.0 and above. No record types or init-only setters are used, ensuring broad compatibility with .NET Framework and .NET Core/5+.

The converter generates traditional classes with public auto-properties. This provides maximum compatibility across .NET versions. You can manually convert to records if you're targeting C# 9+.

When a JSON field is null and the inferred type is a value type (int, double, bool), the converter uses the nullable syntax (int?, double?, bool?). Reference types like string remain as-is since they're inherently nullable.

Yes. All C# property names are automatically converted to PascalCase following .NET naming conventions. For example, a JSON key "first_name" becomes a property named FirstName.

Yes. The converter runs 100% in your browser using client-side JavaScript. Your JSON data is never sent to any server, API, or third-party service. Nothing leaves your machine.

Absolutely. Since all processing happens locally in your browser, you can safely paste API responses, database exports, or any proprietary JSON without privacy concerns.

No. Nothing is persisted. When you close or refresh the page, your input and output are gone. There's no local storage, cookies, or server-side logging of your data.

Your JSON must be valid. Common issues include: missing commas between properties, trailing commas after the last property, unquoted keys (JSON requires double-quoted keys), single quotes instead of double quotes, and missing closing braces or brackets.

This happens when the array is empty ([]). The converter can't infer the element type from zero elements. Add at least one representative element to get proper typing.

The converter uses a 500ms debounce, so it waits until you stop typing before processing. For very large JSON (100KB+), there may be a brief delay after the debounce. The Prettify button can help format your JSON for readability but won't affect conversion speed.

Yes! Contact us through the Contact page or reach out via LinkedIn (linkedin.com/in/racharya404). We actively review feedback and fix issues promptly.