Online C# Compiler

Run C# online in your browser

This is a free online C# playground and compiler. Write C# code directly in your browser, hit Run, and watch mcs compile and Mono execute your program in seconds — no local .NET SDK, no Visual Studio, no dotnet CLI required. It's the fastest way to try a LINQ query, test a generic method, or work through a C# interview problem.

Under the hood, the editor uses the same engine as VS Code (C# syntax highlighting, autocompletion, diagnostic squiggles), and your code compiles with the Mono mcs compiler and runs on Mono 6.12 with the SGen garbage collector. Whether you're exploring LINQ, testing async/await, or prepping for a C# interview, this online C# compiler goes from idea to output in seconds — no csproj to scaffold.

What makes this C# playground useful

• Instant C# execution — write code, press Run, and see output from the online C# compiler in seconds, no dotnet CLI or csproj needed.
• Full C# syntax highlighting, type-aware autocompletion, and clear mcs compile errors — the same editor engine that powers VS Code.
• Stdin input supported — Console.ReadLine(), Console.Read(), and Console.In.ReadToEnd() all read from the playground's input box, so interactive C# programs work end-to-end. No install — no .NET SDK, Visual Studio, Rider, or Mono on your machine.
• Mono 6.12 with the mcs compiler — write C# programs, use LINQ, generics, and async/await without installing the .NET SDK.

What you can build in the C# playground

• LINQ queries — Where, Select, GroupBy, Aggregate over arrays and lists, with the compiler validating your lambdas.
• Classes, interfaces, generics, and pattern matching — core C# idioms you can test one method at a time.
• Quick C# experiments — try an extension method, test an async Task, verify a tuple deconstruction, or confirm how a nullable type flows.

Online C# compiler FAQ