cli

A design guide for command-line programs, which are tools operated through a terminal by typing commands and options. It covers arguments, output, exit codes, configuration, interactive behaviour, and signals.

In plain words
What is it for?
Use it when building, reviewing, debugging, or designing terminal applications, including their options, error messages, configuration, and automation behaviour.
Why use it?
It helps command-line tools behave predictably when people use them directly or connect them to scripts and other programs.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/xobotyi/cc-foundry/cli
Any agent
npx skills add xobotyi/cc-foundry --skill cli
Clone the repo
git clone --depth 1 https://github.com/xobotyi/cc-foundry

Made for: Claude Code, Codex.

Per session 50 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,831 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 2 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00050 $0.02831
Opus 5 $0.00025 $0.01416
Sonnet 5 $0.00010 $0.00566
Haiku 4.5 $0.00005 $0.00283

Measured 2d ago against content hash d02f8c896a89, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

cli scanned grade B with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Asks for rootmediumPrivilege escalation

A mod that escalates privileges can change anything on the machine, not only the project.

- **Be actionable.** Don't say "permission denied" -- say "permission denied; run with sudo or use --config-dir for a

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

- **Lowercase, short, memorable.** `curl` not `DownloadURL`. Use only lowercase letters and hyphens. Keep it easy to
plugins/cli/skills/cli/SKILL.md · 209 lines

How it starts

The opening of the file, as written. The whole thing — 209 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLI Design

Programs are composable by default. stdout carries data, stderr carries diagnostics, exit codes carry status, and signals carry intent. Get the boundaries right and everything else follows.

References

  • Arguments [${CLAUDE_SKILL_DIR}/references/arguments.md] — Full POSIX guidelines, GNU long option table, subcommand patterns, flag design
  • Output [${CLAUDE_SKILL_DIR}/references/output.md] — Stream separation details, color codes, ANSI escapes, NO_COLOR spec, pager setup
  • Exit codes [${CLAUDE_SKILL_DIR}/references/exit-codes.md] — Standard/extended code tables, signal exit codes, partial success patterns
  • Interaction [${CLAUDE_SKILL_DIR}/references/interaction.md] — TTY detection, prompting patterns, confirmation levels, progress display, error format
  • Configuration [${CLAUDE_SKILL_DIR}/references/configuration.md] — Full hierarchy, XDG spec, env var catalog, config file formats, secret handling
  • Signals [${CLAUDE_SKILL_DIR}/references/signals.md] — Full signal table, SIGPIPE handling, crash-only design, child process signals

Output Streams

This is the single most important convention. Mixing data and diagnostics in stdout is the #1 way to break composability.

  • stdout is data. Primary output goes to stdout -- query results, computed values, formatted data. This is what gets piped to the next command or redirected to a file.
  • stderr is diagnostics. Progress indicators, status messages, warnings, errors, and debug output go to stderr. Users see stderr in the terminal even when stdout is redirected.
  • Check each stream independently. stdout may be piped while stderr is still a TTY. Adapt output format per-stream: human-readable when TTY, machine-parseable when piped.
  • No animations when not a TTY. Disable spinners, progress bars, and color when the target stream is not an interactive terminal. This prevents CI logs from becoming escape-code garbage.
  • Print something within 100ms. Before any network request or long operation, print a status line to stderr. Silence looks like a hang.
  • Tell the user what changed. When a command modifies state, describe what happened and suggest what to do next.

Read the full file on GitHub · 209 lines

Files

What ships with it

7 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 209 lines · 50 tokens per session scan B d02f8c896a89

Subscribe to this mod's changes

cli is a skill published in the GitHub repository xobotyi/cc-foundry (20 stars, last pushed 2d ago), licensed MIT. It adds 50 tokens to every session and 2,831 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it B with 2 findings (asks for root, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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