Create CLI

Attribution: Sourced from steipete/agent-scripts by Peter Steinberger.

When to Use

• Designing CLI argument syntax, flags, help text, and output format
• Reviewing CLI UX for human-friendliness and script-compatibility
• Specifying error messages, config handling, and dry-run behavior
• Creating a new command-line tool from scratch

Design CLI surface area (syntax + behavior), human-first, script-friendly.

Reference: https://clig.dev/

Clarify (fast)

Ask, then proceed with best-guess defaults if user is unsure:

• Command name + one-sentence purpose.
• Primary user: humans, scripts, or both.
• Input sources: args vs stdin; files vs URLs; secrets (never via flags).
• Output contract: human text, --json, --plain, exit codes.
• Interactivity: prompts allowed? need --no-input? confirmations for destructive ops?
• Config model: flags/env/config-file; precedence; XDG vs repo-local.
• Platform/runtime constraints: macOS/Linux/Windows; single binary vs runtime.

Deliverables

When designing a CLI, produce a compact spec the user can implement:

• Command tree + USAGE synopsis.
• Args/flags table (types, defaults, required/optional, examples).
• Subcommand semantics (what each does; idempotence; state changes).
• Output rules: stdout vs stderr; TTY detection; --json/--plain; --quiet/--verbose.
• Error + exit code map (top failure modes).
• Safety rules: --dry-run, confirmations, --force, --no-input.
• Config/env rules + precedence (flags > env > project config > user config > system).
• Shell completion story (if relevant): install/discoverability; generation command or bundled scripts.
• 5–10 example invocations (common flows; include piped/stdin examples).

Default Conventions

• -h/--help always shows help and ignores other args.
• --version prints version to stdout.
• Primary data to stdout; diagnostics/errors to stderr.
• Add --json for machine output; consider --plain for stable line-based text.
• Prompts only when stdin is a TTY; --no-input disables prompts.
• Destructive operations: interactive confirmation + non-interactive requires --force or explicit --confirm=....
• Respect NO_COLOR, TERM=dumb; provide --no-color.
• Handle Ctrl-C: exit fast; bounded cleanup; be crash-only when possible.

CLI Spec Skeleton

Fill these sections, drop anything irrelevant:

1. Name: mycmd
2. One-liner: ...
3. USAGE:
   • mycmd [global flags] <subcommand> [args]
4. Subcommands:
   • mycmd init ...
   • mycmd run ...
5. Global flags:
   • -h, --help
   • --version
   • -q, --quiet / -v, --verbose (define exactly)
   • --json / --plain (if applicable)
6. I/O contract:
   • stdout:
   • stderr:
7. Exit codes:
   • 0 success
   • 1 generic failure
   • 2 invalid usage (parse/validation)
8. Env/config:
   • env vars:
   • config file path + precedence:
9. Examples:
   • …

Notes

• Prefer recommending a parsing library (language-specific) only when asked; otherwise keep this skill language-agnostic.
• If the request is "design parameters", do not drift into implementation.