C# Online Editor: Write and Run C# Code Free in Your Browser

Getting started with C# typically means installing Visual Studio (8+ GB), the .NET SDK, and configuring a project structure — a process that can take over an hour. An online C# editor eliminates all of that. Open a browser, write C#, and run it instantly.

tools-online.app provides a free C# editor with syntax highlighting, code execution, AI assistance, and sharing. No Visual Studio, no .NET SDK, no configuration — just C#.

Why Use an Online C# Editor?

C# has one of the heaviest local setup requirements of any language:

• Visual Studio Community: 8+ GB download
• .NET SDK: additional 500 MB+
• Project scaffolding: solution files, project files, NuGet configuration
• Build system: MSBuild configuration and dependency resolution

An online C# editor removes all of that:

• Zero installation — no Visual Studio, no .NET SDK, no disk space
• Instant compilation — write and run C# from any browser
• Cross-platform — code on Windows, Mac, Linux, ChromeOS, or mobile
• Always current — modern C# features without SDK version management
• Privacy-first — your code stays in the browser, never uploaded

Whether you are learning C# fundamentals, practicing LINQ queries, or prototyping a class design, a browser editor gets you coding in seconds.

C# Editor Features

The C# Editor on tools-online.app provides a complete coding environment.

Code Editing

• Syntax highlighting — color-coded keywords, types, strings, comments, attributes, and LINQ expressions
• Line numbers — reference points for compiler error messages
• Auto-indentation — consistent formatting following C# conventions
• Bracket matching — visual pairing for curly braces, parentheses, and angle brackets

Execution and Output

• One-click run — compile and execute with a single button
• Console output — view Console.WriteLine output, exceptions, and stack traces
• Error messages — compiler errors with line numbers and descriptions
• Execution feedback — clear success or failure indication

Sharing and Export

• Share links — generate URLs with your code for team collaboration
• File import — upload existing .cs files from your computer
• Export — download code for local development
• Code samples — pre-loaded examples for quick starts

Getting Started: Your First C# Program

Step 1: Open the Editor

Navigate to tools-online.app/tools/csharp.

Step 2: Write Your Code

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        var products = new List<(string Name, string Category, double Price)>
        {
            ("Laptop", "Electronics", 999.99),
            ("Headphones", "Electronics", 149.99),
            ("Desk Chair", "Furniture", 349.00),
            ("Monitor", "Electronics", 449.99),
            ("Standing Desk", "Furniture", 599.00)
        };

        // Group by category and calculate stats
        var summary = products
            .GroupBy(p => p.Category)
            .Select(g => new
            {
                Category = g.Key,
                Count = g.Count(),
                AvgPrice = g.Average(p => p.Price),
                Total = g.Sum(p => p.Price)
            });

        foreach (var group in summary)
        {
            Console.WriteLine($"{group.Category}: {group.Count} items, " +
                            $"avg ${group.AvgPrice:F2}, total ${group.Total:F2}");
        }
    }
}

Step 3: Run and View Output

Click Run. Output appears in the console below the editor.

Step 4: Iterate and Share

Modify your code, re-run, and use Share to generate a link for colleagues or instructors.

AI-Powered C# Development

The AI assistant accelerates C# coding for beginners and experienced developers alike.

Setup (one-time):

1. Click Settings (lower-left)
2. Add your API key from AIML API
3. Open AI Chat and select a mode

AI capabilities:

• Generate classes — "Create a generic Repository pattern with CRUD operations and async methods"
• Debug errors — paste a compiler error and get a plain-English fix
• Write LINQ — "Convert this foreach loop to a LINQ query with grouping and ordering"
• Explain code — paste complex C# and get a clause-by-clause breakdown
• Design patterns — "Show me the Strategy pattern applied to a payment processing system"

C# Patterns to Practice

LINQ Queries

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

        // Method syntax
        var evenSquares = numbers
            .Where(n => n % 2 == 0)
            .Select(n => n * n)
            .OrderByDescending(n => n);

        Console.WriteLine("Even squares (desc): " +
            string.Join(", ", evenSquares));

        // Query syntax
        var query = from n in numbers
                    where n > 5
                    orderby n descending
                    select $"Value: {n}";

        Console.WriteLine(string.Join(" | ", query));
    }
}

Interfaces and Polymorphism

using System;
using System.Collections.Generic;

interface IShape
{
    double Area { get; }
    string Describe();
}

class Circle : IShape
{
    public double Radius { get; }
    public Circle(double radius) => Radius = radius;
    public double Area => Math.PI * Radius * Radius;
    public string Describe() => $"Circle (r={Radius}, area={Area:F2})";
}

class Rectangle : IShape
{
    public double Width { get; }
    public double Height { get; }
    public Rectangle(double w, double h) { Width = w; Height = h; }
    public double Area => Width * Height;
    public string Describe() => $"Rectangle ({Width}x{Height}, area={Area:F2})";
}

class Program
{
    static void Main()
    {
        var shapes = new List<IShape>
        {
            new Circle(5),
            new Rectangle(4, 6),
            new Circle(3),
            new Rectangle(10, 2)
        };

        foreach (var shape in shapes)
            Console.WriteLine(shape.Describe());

        Console.WriteLine($"\nTotal area: {shapes.Sum(s => s.Area):F2}");
    }
}

Async/Await Patterns

using System;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static async Task<int> SimulateApiCall(string endpoint, int delayMs)
    {
        Console.WriteLine($"Calling {endpoint}...");
        await Task.Delay(delayMs);
        return new Random().Next(100, 1000);
    }

    static async Task Main()
    {
        // Sequential calls
        var start = DateTime.Now;
        var result1 = await SimulateApiCall("/users", 500);
        var result2 = await SimulateApiCall("/orders", 300);
        Console.WriteLine($"Sequential: {result1 + result2} " +
            $"in {(DateTime.Now - start).TotalMilliseconds:F0}ms\n");

        // Parallel calls
        start = DateTime.Now;
        var tasks = new[]
        {
            SimulateApiCall("/products", 400),
            SimulateApiCall("/inventory", 350),
            SimulateApiCall("/pricing", 450)
        };
        var results = await Task.WhenAll(tasks);
        Console.WriteLine($"Parallel: {results.Sum()} " +
            $"in {(DateTime.Now - start).TotalMilliseconds:F0}ms");
    }
}

Dictionary and Collections

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        var wordCount = new Dictionary<string, int>();
        string text = "the quick brown fox jumps over the lazy dog the fox";

        foreach (var word in text.Split(' '))
        {
            if (wordCount.ContainsKey(word))
                wordCount[word]++;
            else
                wordCount[word] = 1;
        }

        Console.WriteLine("Word frequencies:");
        foreach (var pair in wordCount.OrderByDescending(p => p.Value))
            Console.WriteLine($"  {pair.Key}: {pair.Value}");

        Console.WriteLine($"\nUnique words: {wordCount.Count}");
        Console.WriteLine($"Most common: {wordCount.MaxBy(p => p.Value).Key}");
    }
}

Who Uses Online C# Editors?

Students Learning C#

Practice fundamentals — classes, interfaces, LINQ, generics — without installing Visual Studio. Sample code runs instantly for coursework and lab assignments.

.NET Developers

Quick-test a LINQ query, validate a pattern implementation, or prototype a utility class without opening a full solution.

Interview Candidates

Practice C# coding challenges — algorithm problems, string manipulation, collection operations — in a realistic editor environment.

Educators

Create and share code examples via URL. Students open the link and run the code immediately, with no classroom setup required.

Cross-Platform Developers

Code C# from Mac, Linux, or Chromebook without the Windows-centric Visual Studio installation.

Online C# Editor vs Visual Studio

Tips for Productive C# Coding Online

1. Start with sample code — load templates to see working C# patterns
2. Use AI for boilerplate — generate class skeletons, properties, and constructors
3. Practice LINQ — the editor is perfect for experimenting with query expressions
4. Read compiler errors — C# error messages include codes (CS0001) and descriptions that guide fixes
5. Test incrementally — compile after each class or method, not after writing an entire program
6. Share for feedback — generate a link and send to peers for code reviews

Related C# and Development Resources

Code Editors on tools-online.app:

• C# Editor — Write and run C# code online
• Java Editor — Java development environment
• TypeScript Editor — TypeScript coding with execution
• Python Editor — Python development environment

Development Resources:

• Online Code Tools — 15+ programming language editors
• Code Compare Tool — Compare C# file versions
• AI Integration Guide — Set up AI-powered coding assistance

FAQs

How do I run C# code online?

Visit tools-online.app/tools/csharp, write your code, and click Run. No account, .NET SDK, or installation needed.

What C# features are supported?

The editor supports classes, interfaces, generics, LINQ, async/await, records, pattern matching, nullable types, and standard .NET library imports.

Can AI write C# code for me?

Yes. The AI assistant generates classes, LINQ queries, design pattern implementations, and algorithm solutions from natural language descriptions.

Is my code private?

Yes. All code editing happens locally in your browser. Nothing is uploaded to external servers.

Do I need Visual Studio or .NET SDK?

No. The editor works entirely in your browser with zero local software requirements.

Can I import .cs files?

Yes. Use the file import feature to upload C# files from your computer.

Is this good for C# interviews?

Yes. Practice algorithm problems, LINQ challenges, and OOP design questions with instant compilation and AI hints.