C# Eval Expression Overview

What is the C# Eval Expression library?

The C# Eval Expression library is the most powerful and flexible expression evaluators you can find. It supports almost all the C# language and gets improved every year (See our Release Notes). The library also includes multiple built-in logic features to make it easier for you to work with and evaluate C# dynamic expressions.

You can use this library to evaluate from simple math expressions to very complex C# code.

Do not worry if that is still unclear. We will explain everything you need to know about what this library can do in this Getting Started. But in a very simple example, it allows you to do something like this:

// @nuget: Z.Expressions.Eval
using Z.Expressions;

var x = "1+2".Execute<int>(); // returns 3

That is sure a straightforward example, but imagine the string is not just 1+2, but any C# code containing keywords such as if, foreach, or even LINQ methods. Would that not be awesome, right? Well, that is exactly what this library allows you to do.

Installing the C# Eval Expression library

You can download the C# Eval Expression library from NuGet: https://www.nuget.org/packages/Z.Expressions.Eval/

You can also visit our download page to find all available links.

PM> Install-Package Z.Expressions.Eval

dotnet add package Z.Expressions.Eval

What is an expression evaluator?

An expression evaluator is a library that allows you to execute an expression and get a result. This is especially useful for math expressions, but you can also take advantage of an expression evaluator in many other scenarios, such as:

  • Creating HTML forms at runtime
  • Applying dynamic validation rules
  • Dynamically filtering a report (users enter their own filtering or ordering logic)
  • Setting different environments per user
  • Or even using it in a Discord bot to return the result of an expression

The possibilities of how you can use an expression evaluator are almost infinite. The more you understand the library, the more new use cases you will discover.

For example, you can evaluate a simple math expression like this:

// @nuget: Z.Expressions.Eval
using Z.Expressions;

int result = Eval.Execute<int>("X + Y", new { X = 1, Y = 2 });

But you can also execute much more complex code, such as creating a list dynamically and filtering it using LINQ methods:

// @nuget: Z.Expressions.Eval
using Z.Expressions;

int result = Eval.Execute<int>(@"
    var list = new List<int>() { 1, 2, 3, 4, 5 };
    var filter = list.Where(x => x < 4);
    return filter.Sum(x => x);
");

What does the C# Eval Expression support?

The C# Eval Expression library is compatible with the following platforms:

  • .NET 5+
  • .NET Core 2+
  • .NET Framework 4.0+

It supports nearly everything, from basic keywords to more advanced C# language features, including:

  • Anonymous types
  • Extension methods
  • Lambda expressions
  • LINQ methods
  • Method overloads

The library also includes many useful features, such as:

  • SafeMode: Evaluate expressions in a secure environment
  • RegisterKeyword: Register your own keyword to apply custom logic
  • AddMethod: Create methods dynamically to reuse them in your expressions

The library also includes multiple built-in logic behaviors. For example, it automatically calls the ToList method when the expected return type is a list, but the expression returns an IEnumerable.

It also handles object values with built-in logic that allows you to go deeper in your expressions and go beyond some C# language limitations.

Finally, some additional keywords have been added, such as break all. This keyword breaks all loops instead of only the current one.

Is C# Eval Expression free?

Yes and no.

C# Eval Expression is free when:

  • The expression is up to 50 characters
  • You use any LINQ Dynamic methods

For commercial usage, we recommend always purchasing a license.

The library is also included in commercial products such as Entity Framework Extensions and Dapper Plus.

Summary

In this Getting Started section, you learned the basics of what an expression evaluator is and how to use it.

For developers who want to learn more about the C# Eval Expression library—or for those who already understand the basics—we highly recommend reading and completing all of the following Getting Started sections:

Last updated: 2026-02-19
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