CLI Design Expert

Use this skill to design, refactor, or audit CLIs that are:

• Human-friendly for interactive use
• Predictable in scripts and CI
• Safe for destructive operations
• Clear in output, errors, and exit semantics

Primary reference: references/CLI_GUIDELINES.md.

Working stance

Be direct and engineering-first. If a design is fragile, ambiguous, or hostile to automation, call it out and propose concrete fixes.

Non-negotiable checks (fast fail)

Treat any failure below as P0.

1. Non-interactive path is required

• Never make an interactive prompt the only input path.
• Every prompt needs a non-interactive alternative (flag/arg/file/stdin).
• If stdin is not a TTY, do not prompt. Fail with actionable guidance and required flags.
• Provide --no-input (or equivalent) to disable prompts.

1. Secrets safety

• Never accept secrets via flags (leaks via ps and shell history).
• Prefer stdin, --secret-file, OS keychain, or a TTY-only prompt with a non-interactive alternative.

1. Scriptability and CI behavior

• Detect TTY and adapt output and interactivity.
• Disable spinners/animations when stdout is not a TTY.
• Disable color when stdout/stderr are not TTY, when NO_COLOR is set, when TERM=dumb, or when --no-color is passed.
• Keep stdout clean for data; send status/progress/logging to stderr.

1. Output streams and exit codes

• Primary pipeable output goes to stdout.
• Logs, warnings, progress, and errors go to stderr.
• Exit 0 on success; non-zero on failure. Map non-zero codes to meaningful failure categories.

1. Risk-scaled safeguards

• For destructive actions, use confirmations that scale with risk.
• Support a scriptable bypass (e.g., --force or --yes), and consider --confirm="resource-name" for severe actions.
• Offer --dry-run for risky or complex state changes when possible.

1. Signals and cancellation

• Ctrl-C (SIGINT) should exit quickly with immediate feedback.
• Timebox cleanup and allow a second Ctrl-C to force exit if cleanup is slow.

Quick triage questions

• Who is the user: interactive human, script/CI, or both?
• What is the job-to-be-done: query/list state, or change state?
• What are the core objects and verbs?
• What must stay stable for automation (output format, exit codes, flags)?

Procedure: Design a new CLI (or add a command)

Step 1: Propose a command model

• Keep the initial surface area small.
• Choose one model and stay consistent:
• Single command + flags for simple tools.
• Subcommands (often noun-verb or verb-noun) for multi-task tools.

Deliverable:

• List of commands with one-line purposes.

Step 2: Decide positional args vs flags

Heuristic:

• Use positional args only for obvious primary object(s) where order is standard and unambiguous.
• If two positionals can be confused (similar shape/meaning) or order is not obvious, use flags instead.
• Prefer long flags. Use short flags only for the most common options, and keep them consistent across commands.

Deliverable:

• Usage line + args/flags tables per command.

Step 3: Define output contract (human + machine)

• Define exactly what goes to stdout vs stderr.
• Provide at least one machine-readable mode when helpful (commonly --json).
• Keep human-readable output scannable and useful.

Deliverable:

• stdout content
• stderr content
• Exit-code map
• High-level --json schema (if supported)

Step 4: Write help text and examples

• -h/--help must work even when other args are wrong.
• If run incorrectly, show a short error + the relevant usage + "use --help".
• Lead help with examples (common first). Provide a docs/support path in top-level help.

Deliverable:

• Draft help text for top-level and relevant subcommands.

Step 5: Define errors and safety

• Errors must be actionable: what failed, why, and how to fix it.
• Do not hide important failures behind generic codes or stack traces unless --debug is enabled.
• For state changes, give explicit feedback about what happened (or what would happen in --dry-run).

Deliverable:

• Error-message patterns + safety/confirmation design.

Step 6: Specify interactivity and TTY rules

• Only prompt when stdin is a TTY.
• If piped input is supported, read it. If not, fail quickly with guidance.
• Provide clear quiet and verbose modes if logs exist.

Deliverable:

• TTY behavior table (TTY vs non-TTY).

Step 7: Add config and env vars (only if needed)

Use explicit precedence to avoid hidden config behavior:

1. Flags
2. Environment variables
3. Project-level config
4. User-level config (XDG, e.g. ~/.config/<tool>/config)
5. System-wide config

Deliverable:

• Config keys + precedence + storage locations.

Procedure: Review an existing CLI

Produce two outputs.

A) Scorecard (0-2 each)

• Command structure and naming
• Args/flags clarity
• Help discoverability (examples first)
• stdout/stderr correctness
• Exit-code discipline
• Scriptability (non-TTY behavior)
• Machine-output mode (when appropriate)
• Safety (--dry-run, confirmations)
• Secrets handling
• Signal handling (Ctrl-C)
• Config precedence (if applicable)
• Future-proofing (avoid time bombs)

B) Prioritized fixes

• P0: correctness, safety, and scriptability failures
• P1: usability and discoverability issues
• P2: polish and consistency

Templates

Help skeleton

NAME -

USAGE [options]

EXAMPLES ... ... --json | jq .

OPTIONS -h, --help Show help --json Output machine-readable JSON (if supported) --no-color Disable color --no-input Disable prompts -q, --quiet Reduce non-essential output (if supported) -v, --verbose Increase logging (if supported) -n, --dry-run Describe changes without applying them (if supported)

SUPPORT <docs / issues link>

Error skeleton

Error: . Cause: . Fix: <exact next step / command / flag>.

References

• Full guideline text: references/CLI_GUIDELINES.md

Update Check

On first use in a session, silently check for a newer version:

1. Fetch https://raw.githubusercontent.com/abpai/skills/main/versions.json.
2. Compare the version for cli-design-expert against this file's metadata.version.
3. If the remote version is newer, pause before the main task and ask:

   cli-design-expert update available (local {X.Y} → remote {A.B}). Would you like me to update it for you first? I can run npx skills update cli-design-expert for you.

4. If the user says yes, run the update before continuing.
5. If the user says no, continue with the current local version.
6. If the fetch fails or web access is unavailable, skip silently.