CLI framework for C# (.NET): System.CommandLine and Spectre.Console

CLI framework for C# (.NET): System.CommandLine and Spectre.Console

Creating high-quality console applications (CLI) in C# is a task that requires not only command-line argument parsing, but also convenient data presentation, subcommand support, validation, and interactivity. In the .NET ecosystem, there are two powerful tools for this: the official System.CommandLine from Microsoft and the versatile library Spectre.Console. In this article, we will thoroughly examine their capabilities, show usage examples, and compare approaches.

1. System.CommandLine: official parser from Microsoft

System.CommandLine is an open-source library that provides a declarative way to define commands, arguments, options, and handlers. It is part of the .NET SDK (starting from .NET 6) and is available as a NuGet package.

Key features

• Declarative description of command structure using attributes or fluent API.
• Automatic help generation (--help).
• Support for nested commands (subcommands) and aliases.
• Validation of arguments and options (types, ranges, required).
• Integration with DI containers and middleware.

Example: simple application with two commands

Let's create a console application that supports greet and calc commands.

using System.CommandLine;

var rootCommand = new RootCommand("Multi-functional CLI application");

// greet commandvar greetCommand = new Command("greet", "Greet the user");var nameOption = new Option<string>(    "--name",    () => "world",    "Name for greeting");greetCommand.AddOption(nameOption);

greetCommand.SetHandler((string name) =>{    Console.WriteLine($"Hello, {name}!");}, nameOption);

// calc commandvar calcCommand = new Command("calc", "Simple calculator");var aArgument = new Argument<int>("a", "First number");var bArgument = new Argument<int>("b", "Second number");var operationOption = new Option<string>(    "--operation",    () => "add",    "Operation: add, sub, mul, div");calcCommand.AddArgument(aArgument);calcCommand.AddArgument(bArgument);calcCommand.AddOption(operationOption);

calcCommand.SetHandler((int a, int b, string op) =>{    var result = op switch    {        "add" => a + b,        "sub" => a - b,        "mul" => a * b,        "div" => b != 0 ? a / b : throw new DivideByZeroException(),        _ => throw new ArgumentException("Unknown operation")    };    Console.WriteLine($"Result: {result}");}, aArgument, bArgument, operationOption);

rootCommand.AddCommand(greetCommand);rootCommand.AddCommand(calcCommand);

return await rootCommand.InvokeAsync(args);

Running the application:

dotnet run -- greet --name "PythonLib"dotnet run -- calc 10 5 --operation mul

2. Spectre.Console: beauty and interactivity

Spectre.Console is a library for creating beautiful console interfaces. It does not replace an argument parser, but perfectly complements it: colored output, tables, progress bars, interactive menus, and even drawing in the console.

Key features

• Colored and formatted output with Markdown support.
• Tables, charts, calendars.
• Interactive components: list selection, text input, confirmation.
• Animation (spinners, progress bars).
• Drawing borders, panels, and columns.

Example: interactive menu and table

Let's show how to create a selection menu and display data in a table format.

using Spectre.Console;

// Interactive menuvar choice = AnsiConsole.Prompt(    new SelectionProm