Dynamic Object (ExpandoObject) Builder

Build a C# dynamic ExpandoObject from sample JSON or key-value pairs free online. Generates ready-to-paste code for ASP.NET projects that need flexible objects.

Sample JSON or key-value data

How to Use This Tool

Paste sample JSONAdd the JSON shape you want represented as a dynamic object

Set a variable nameChoose what the generated C# variable should be called

Generate and copyGet ready-to-paste ExpandoObject code for your project

When You Don't Know the Shape of Your Data Until Runtime

Most of the time in C#, you know your data's structure ahead of time and define a class for it. Sometimes you genuinely don't — building a response object that varies by request, working with truly dynamic configuration, or prototyping before the final shape is locked down. ExpandoObject exists for exactly this situation, letting you build an object property by property at runtime.

Writing the ExpandoObject assignment code by hand for anything beyond a couple of fields gets repetitive fast. This tool takes sample JSON representing the shape you want and generates the actual C# code: the ExpandoObject declaration followed by every property assignment needed to match your sample.

Dot Notation Without Giving Up Flexibility

The appeal of ExpandoObject over a plain Dictionary is syntax. Once cast to dynamic, obj.name reads naturally in code, closer to how you would access a real class property, while still allowing properties to be added or changed at runtime without a fixed class definition constraining you.

Nested Structures Generate Nested Objects

When your sample JSON has a nested object, like an address field containing city and zip, the generated code creates a separate ExpandoObject for that nested structure and assigns it to the parent property, mirroring exactly how the source data was organized rather than flattening everything into one level.

Frequently Asked Questions

ExpandoObject lets you add, remove, and access properties dynamically at runtime without defining a fixed class beforehand. It is commonly used when the shape of data isn't known until runtime, like building a flexible API response or working with loosely structured configuration data.

A Dictionary requires bracket syntax like dict['name'] to access values. ExpandoObject lets you use dot notation like obj.name once cast to dynamic, which often reads more naturally and works better with certain serialization and templating scenarios.

It generates working C# code: dynamic obj = new ExpandoObject(); followed by the assignment lines needed to set every property to match the JSON or key-value pairs you provided.

Yes, nested JSON objects generate nested ExpandoObject instances assigned to the parent property, preserving the same structure your source JSON had.

If your data shape is known and stable, a regular class gives you compile-time type checking and better IDE support. ExpandoObject is the right tool specifically when the shape is genuinely unknown or varies at runtime — using it for fixed, predictable data trades away safety for flexibility you don't actually need.