# clap

This skill guides Rust CLI work with Clap, including subcommands, layered settings, exit codes, completions, and binary tests.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 331 installs · ★ 78
- Author: Claude MPM Team
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/bobmatnyc/claude-mpm-skills/tree/HEAD/toolchains/rust/cli/clap/SKILL.md
- Updated: 2026-07-18
- HTML: https://affpapa.org/en/nevibecode/skills/clap

## What it does

This skill gives an agent a clear pattern for building Rust command-line tools with Clap. It covers derive-based argument types, shared flags, subcommands for separate modes, and a single parsing step in `main`. The examples also cover validation and help output, so command behavior stays visible to users.

Settings can be resolved across four layers: CLI values first, then environment variables, a config file, and defaults. Command handlers return `Result`, while the top level prints errors and maps failures to stable exit codes. `assert_cmd` is used to test the binary through arguments, output, and status; `clap_complete` can emit Bash, Zsh, or Fish completions. Keep parsing in `main`, since parsing inside library code makes the design harder to test and reuse.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill clap -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/clap/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/clap/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill clap -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/clap/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill clap -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/clap/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install bobmatnyc/claude-mpm-skills clap
```

2. **Manually: put the files in place**
- File: `.github/skills/clap/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill clap -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/bobmatnyc/claude-mpm-skills --path toolchains/rust/cli/clap
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/clap/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill clap -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/bobmatnyc/claude-mpm-skills/tree/HEAD/toolchains/rust/cli/clap/SKILL.md

## When to use it
- design a Rust CLI around subcommands
- merge CLI, environment, and file configuration
- map command failures to stable exit codes
- test help, output, and arguments through the binary
- emit shell completions for a command-line tool

## Example prompts
- Build a Rust Clap CLI with `serve` and `migrate` subcommands, a shared `--verbose` flag, and `MYTOOL_CONFIG` support.
- Set configuration precedence to CLI arguments, environment variables, a config file, then defaults.
- Add `assert_cmd` integration tests for `--help`, command output, and failure status.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: bd4370c177e4253e.

BEGIN THIRD-PARTY FILE bd4370c177e4253e
````text
---
name: clap
description: "Build production Rust CLIs with Clap: subcommands, config layering, validation, exit codes, shell completions, and testable command surfaces"
user-invocable: false
disable-model-invocation: true
version: 1.0.0
category: toolchain
author: Claude MPM Team
license: MIT
progressive_disclosure:
  entry_point:
    summary: "Create ergonomic, testable Rust CLIs using Clap derive, subcommands, and config layering (CLI + env + config file)"
    when_to_use: "When building Rust CLI tools that need reliable argument parsing, good help UX, strong validation, and automated tests"
    quick_start: "1. Add clap (derive) 2. Define Args + Subcommand 3. Parse once in main 4. Map errors to exit codes 5. Test with assert_cmd"
  token_estimate:
    entry: 120
    full: 4500
context_limit: 700
tags:
  - rust
  - cli
  - clap
  - config
  - testing
requires_tools: []
---

# Clap (Rust) - Production CLI Patterns

## Overview

Clap provides declarative command-line parsing with strong help output, validation, and subcommand support. Use it to build CLIs with predictable UX and testable execution paths.

## Quick Start

### Minimal CLI

✅ **Correct: derive Parser**
```rust
use clap::Parser;

#[derive(Parser, Debug)]
#[command(name = "mytool", version, about = "Example CLI")]
struct Args {
    /// Enable verbose output
    #[arg(long)]
    verbose: bool,

    /// Input file path
    #[arg(value_name = "FILE")]
    input: String,
}

fn main() {
    let args = Args::parse();
    if args.verbose {
        eprintln!("verbose enabled");
    }
    println!("input={}", args.input);
}
```

❌ **Wrong: parse multiple times**
```rust
fn main() {
    let _a = Args::parse();
    let _b = Args::parse(); // duplicate parsing and inconsistent behavior
}
```

## Subcommands (real tools)

Model multi-mode CLIs with subcommands and shared global flags.

✅ **Correct: global flags + subcommands**
```rust
use clap::{Parser, Subcommand, ValueEnum};

#[derive(Parser, Debug)]
struct Args {
    #[arg(long, global = true)]
    verbose: bool,

    #[arg(long, global = true, env = "MYTOOL_CONFIG")]
    config: Option<String>,

    #[command(subcommand)]
    cmd: Command,
}

#[derive(Subcommand, Debug)]
enum Command {
    Serve { #[arg(long, default_value_t = 3000)] port: u16 },
    Migrate { #[arg(long, value_enum, default_value_t = Mode::Up)] mode: Mode },
}

#[derive(Copy, Clone, Debug, ValueEnum)]
enum Mode { Up, Down }

fn main() {
    let args = Args::parse();
    match args.cmd {
        Command::Serve { port } => println!("serve on {}", port),
        Command::Migrate { mode } => println!("migrate: {:?}", mode),
    }
}
```

## Config layering (CLI + env + config file)

Prefer explicit precedence:

1. CLI flags
2. Environment variables
3. Config file
4. Defaults

✅ **Correct: merge config with CLI overrides**
```rust
use clap::Parser;
use serde::Deserialize;

#[derive(Parser, Debug)]
struct Args {
    #[arg(long, env = "APP_PORT")]
    port: Option<u16>,
}
````
END THIRD-PARTY FILE bd4370c177e4253e

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