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dotnet-cli-parsing

Implements CLI argument parsing for .NET console apps and global tools using System.CommandLine 2.0 GA.

2|Updated Aug 2, 2026
Search Tags:#csharp#cli#dotnet#mcp server#argument parsing#system.commandline#console app
One-click install
npx skills add https://github.com/Arasz/ai-raccoon --skill dotnet-cli-parsing-arasz
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: dotnet-cli-parsing
Source: https://github.com/Arasz/ai-raccoon/tree/main/.ai-badger/skills/learned/uncategorized/dotnet-cli-parsing
Command: npx skills add https://github.com/Arasz/ai-raccoon --skill dotnet-cli-parsing-arasz

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill requires System.CommandLine, and includes references (resource) components.

What problem does it solve? Adding command-line argument parsing to .NET console apps and global dotnet tools is full of traps: the System.CommandLine 2.0 GA API differs sharply from the beta API most blog posts show, help text leaks into stdout and corrupts stdio MCP/JSON-RPC protocol streams, and parse-first entry points break WebApplicationFactory-based E2E tests. This Skill provides empirically verified, version-pinned guidance so these mistakes are avoided. ## Core Features & Use Cases - Parser selection guidance: Compares System.CommandLine 2.0.x GA, Spectre.Console.Cli, Microsoft.Extensions.Configuration.CommandLine, Cocona (archived), and McMaster.Extensions.CommandLineUtils with verified version and status data. - Pinned System.CommandLine 2.0.10 GA idioms: Parse-first patterns, help/version action detection, instance-based option reads via GetValue<T>(Option<T>), Option.Validators for custom value grammars, duplicate-alias handling, and the two-root pattern for optional subcommands. - Protocol-stream and test-host traps: Routes all CLI output to stderr for stdio MCP servers, declares hidden no-op options for WebApplicationFactory's injected flags, and covers secrets policy, wildcard shell-expansion diagnostics, and config-verb trees. - Use Case: When adding a serve subcommand with --port and --idle-timeout options to a .NET MCP server, use this Skill to wire parse-first argument handling, validate values with Option.Validators, keep help off stdout, and keep WebApplicationFactory E2E tests green. ## Quick Start Use the dotnet-cli-parsing skill to add System.CommandLine 2.0 GA argument parsing with stderr-safe help rendering to my .NET console app.

Frequently Asked Questions about dotnet-cli-parsing

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I parse command-line arguments in a .NET console app?▼

Use System.CommandLine 2.0.x GA, the default choice for flat option sets. Call root.Parse(args, new ParserConfiguration { EnablePosixBundling = true }) directly — the beta CommandLineBuilder and UseDefaults() APIs no longer exist in GA.

System.CommandLine vs Spectre.Console.Cli — which should I use?▼

System.CommandLine 2.0.x is GA, MIT-licensed, dependency-free on net8.0, and used by the dotnet CLI itself, making it the default for flat option sets. Spectre.Console.Cli is a full command framework with DI and nested commands, which is overkill for roughly ten flat options.

Why does System.CommandLine help output break my stdio MCP server?▼

System.CommandLine renders help to stdout by default, which corrupts a JSON-RPC protocol stream on stdout. Fix it by invoking with parseResult.Invoke(new InvocationConfiguration { Output = writer, Error = writer }) where both writers are Console.Error, and pin it with a test asserting zero bytes reach stdout.

Why does WebApplicationFactory fail after switching to parse-first CLI parsing?▼

WebApplicationFactory invokes the real entry point with --environment, --contentRoot, and --applicationName arguments, which a parse-first entry point rejects as unknown options. Declare the three as hidden no-op options on the root command so the triplet parses with zero errors.

How do I validate custom option values in System.CommandLine 2.0 GA?▼

Option.Validators is the only native parse-error hook in GA — there is no ParseArgument or ErrorMessage property. Add a validator delegate that reads the raw token with result.GetValueOrDefault<string>() and reports failures via result.AddError("...").

Can a root command with subcommands be invoked without a verb?▼

No — a RootCommand with subcommands cannot be invoked bare in 2.0.10 GA; parsing flags without a verb yields "Required command was not provided." The working pattern builds two roots over the same options: a full tree for help and verbs, and a launch-only root for verb-less flag sets.

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