Run C# Online

Program.cs

// C# (.NET 9) — top-level statements
using System.Linq;

Console.WriteLine("Hello from C#!");

// LINQ — modern data pipeline
var numbers = Enumerable.Range(1, 10);
var squares = numbers.Select(n => n * n).ToArray();
Console.WriteLine($"Squares: [{string.Join(", ", squares)}]");

// Records — value semantics in 1 line
record Point(int X, int Y);
var p = new Point(3, 4);
Console.WriteLine($"Point: {p}, distance from origin: {Math.Sqrt(p.X * p.X + p.Y * p.Y):F2}");

Output

Click "Run Code" to execute...

About C#

C# is Microsoft's flagship language and now fully cross-platform via .NET 9. Top-level statements, records, pattern matching, and LINQ make it one of the most productive languages for everything from web APIs to game development with Unity.

Our sandbox runs .NET 9 with the BCL. dotnet add package is available in Pro+ sessions.

Sandbox Features

Secure execution with Docker + gVisor isolation
C# .NET 9 with standard library
Up to 600s execution time (Mega tier)
Stdin, expected_output, command_line_arguments
Stateful sessions and package install (Pro+)
REST API for programmatic access

Use C# with stateful sessions

Open a session once, then call execute repeatedly — variables, files, and installed packages persist between runs. Perfect for code interpreters and REPL-style agents.

# 1. Create a session
curl -X POST https://api.sandboxapi.dev/v1/sessions \
  -H "X-RapidAPI-Key: $KEY" \
  -d '{"language":"csharp","idle_ttl":300}'
# → {"id":"sess_abc","language":"csharp",...}

# 2. Execute — first call
curl -X POST https://api.sandboxapi.dev/v1/sessions/sess_abc/execute \
  -H "X-RapidAPI-Key: $KEY" \
  -d '{"code":"int x = 42; Console.WriteLine(x);"}'

# 3. Execute again — state carries over
curl -X POST https://api.sandboxapi.dev/v1/sessions/sess_abc/execute \
  -H "X-RapidAPI-Key: $KEY" \
  -d '{"code":"// Note: C# is compiled — sessions persist files, not REPL state"}'

Note: C# is a compiled language. Sessions persist installed packages and files on disk, but variable state does not carry between calls. Use multi-file submissions or write intermediate state to disk.

Read the sessions docs →

About C#

Sandbox Features

Use C# with stateful sessions

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