C# Dynamic vs Object: Key Differences Every Dev Should Know

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Introduction: Confused by dynamic and object in C#? You’re Not Alone!

In C# applications, you may have used dynamic and object types. They both look similar at first glance. Both can hold any data type, and both are flexible. So what’s the real difference between dynamic and object in C#?

In this blog, we will break down the differences between dynamic and object. We will also explore the practical API scenarios which focus on model binding and JSON serialization. We will also discuss which is faster, safer, and easier to maintain.

At the end of this blog, you will understand when to use dynamic and object in a C# application.

What are dynamic and object in C#?

Before we explore practical API scenarios, it’s important first to understand the meanings of dynamic and object in C#.

object – The Base of All Types

In C#, every type inherits from the base object type. That means you can store any value in a variable of type object.

object obj= 25; // Holds an int
obj= "Hello dotnet infinity";   // Now holds a string

But here’s the catch: when using an object, you often need to cast it back to its original type before using it:

object obj = "Hello dotnet infinity";
string txt= (string)obj; // Requires explicit casting

dynamic – Type Checking Happens at Runtime

Dynamic type was introduced in C# 4.0. The dynamic type bypasses compile-time type checking. This means you can call properties and methods on it that the compiler doesn’t validate, but the program may crash at runtime if you’re wrong.

dynamic dyn = "Hello";
Console.WriteLine(dyn.Length); // Works
Console.WriteLine(dyn.NonExistentMethod()); // Runtime error!

Key Differences Between dynamic and object in C#

Feature	object	dynamic
Type Checking	Compile-time	Runtime only
IntelliSense	Full	None
Performance	Faster	Slower
Error Detection	Compile-time	Runtime
Maintainability	High	Low
Flexibility	Medium	High
Best Use Case	Known types, APIs	Unknown structure JSON

Real-World Example

Model Binding from JSON

Suppose your API accepts JSON from a client. If you don’t know the exact structure of the incoming data, what do you use?

Example Using dynamic (Good for unknown JSON structure)

[HttpPost("AddUser")]
public IActionResult AddUser([FromBody] dynamic data)
{
    string firstName = data.FirstName; // No compile-time check
    string lastName= data.LastName; 
    return Ok($"Received FirstName: {firstName}, LastName: {lastName}");
}

This works if the JSON has those fields, but will crash if data.FirstName or data.LastName doesn’t exist.

Example Using object + Deserialization (Better safety)

[HttpPost("AddUser")]
public IActionResult AddUser([FromBody] object payload)
{
    var json = JsonSerializer.Serialize(payload);
    var user = JsonSerializer.Deserialize<UserModel>(json);
    return Ok($"Received FirstName: {user.FirstName}, LastName: {user.LastName}");
}

Here, the object is deserialized to a strong type, providing type safety and cleaner error handling.

public class UserModel
{
    public string FirstName{ get; set; }
    public string LastName{ get; set; }
}

Use Cases: object vs dynamic in C#

Use Case	Use object	Use dynamic
Public API request/response models	Ensures type safety and validation	Avoid – lacks compile-time validation
Flexible or unknown JSON from third-party API	Verbose – needs manual parsing or custom model	Easy access to properties at runtime
Internal tools/prototypes	Use when you can define models	Acceptable for quick JSON or dynamic data
Temporary storage for different types	Store as object, cast back when needed	Overkill – unnecessary overhead
Serialization/Deserialization scenarios	Use strongly typed models for predictable schema	Use for unstructured JSON or loosely defined schemas
COM interop / Office automation	Verbose and complex with object	Preferred for dynamic runtime interactions
Reflection-based property access	Controlled, but more verbose with type checking	Cleaner, but riskier – depends on accurate member names
Plugin architectures / dynamic scripting	Not flexible enough for dynamic method/property calls	Excellent for runtime extensibility
Working in large teams or enterprise projects	More maintainable, testable, and readable	Can cause hidden bugs and make code harder to maintain
Rapid JSON manipulation (e.g. admin dashboards)	Slower and needs mapping	Faster iteration, especially in internal or trusted scenarios

Conclusion

Understanding the difference between dynamic and object in C# is crucial for building clean, safe, and high-performance code.

Use object when you want: type safety, performance, and maintainability.
Use dynamic when you need: flexibility, unknown data structures, or dynamic language interop.

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