AI Friendly CLI Design

AI-Friendly CLI Design

Use this skill when public CLI behavior affects how an Agent discovers safe usage, runs a command, reads the result, recovers from failure, or chooses the next action.

Core judgment:

A CLI command is not only an execution surface. It is a context delivery surface for the next Agent step.

Golden Principles

Help is part of the interface. A command's help should explain why an Agent would call it, what input shape it expects, what output modes exist, what can go wrong, and what a likely next step looks like.

Output is context, not just result. Normal output should carry enough state for an Agent to continue without reconstructing hidden context.

Defaults should be token-aware. Repeated Agent loops need useful, bounded output by default; detail should be opt-in and discoverable.

JSON stdout is a contract. Machine-readable output must stay parseable, stable, and free of logs, banners, or prose.

Ambiguity belongs in the output. If a command is matching, guessing, filtering, truncating, or returning candidates, say so directly.

Errors are guidance. A useful error names the failed input, explains the expected shape, and exits non-zero.

Large artifacts belong in files. Print a path, summary, validation status, and next command instead of flooding the context window.

Good CLI Signals

Good Agent-facing commands usually have:

• copyable examples with realistic identifiers;
• a concise default output with result, completeness signal, and next action;
• --format json for automation;
• --output <path> for large or durable artifacts;
• pagination or filters for long collections;
• clear candidate lists instead of silent fuzzy selection;
• stderr for diagnostics that must not pollute structured stdout;
• tests for help text, JSON shape, pagination, file output, and actionable errors.

CLI Smells

Help smells:

• Help only lists flags and never explains when to use the command.
• Examples hide the real input shape behind vague placeholders.
• Machine-readable and human-readable modes are not distinguished.

Output smells:

• Normal output is decorative, noisy, or too large for repeated Agent loops.
• The result does not say whether it is complete, partial, filtered, paginated, or ambiguous.
• The next action is missing, vague, or only says to review carefully.
• JSON output is mixed with warnings, logs, npm banners, or progress text.

Behavior smells:

• The command silently chooses among ambiguous candidates.
• Default behavior depends on private workspace state, aliases, untracked files, or hidden configuration.
• A command writes durable or network-visible changes without making the action explicit.
• --verbose is required for normal decision-making.

Error smells:

• The error says only Invalid input.
• Missing, malformed, unsupported, and ambiguous inputs all fail the same way.
• The command exits successfully after failing to do the requested work.

Design Moves

When improving a CLI, prefer these moves:

• Put the result first, context second, and next action last.
• Add a compact Summary and Next block to human-readable output.
• Add explicit completeness fields to JSON: pagination, truncation, filters, candidates, warnings, or confidence.
• Move logs and diagnostics to stderr when stdout may be parsed.
• Add --output <path> for generated reports, drafts, bundles, or other long artifacts.
• Show the exact command to continue pagination or inspect a written artifact.
• Return candidates with match reasons instead of guessing when resolution is unsafe.
• Add targeted tests around public behavior whenever help, output shape, or exit behavior changes.

Human Output Shape

Use this shape when a command has a natural next step:

<short result title>

Summary:
- <what was selected, created, changed, returned, or validated>
- <completeness, pagination, filtering, ambiguity, or failure note>

Next:
- <one or two likely next commands or decisions>

Do not force the shape when a one-line result is clearer.

CLI Design Notes

When helping design or diagnose a CLI, keep the response compact:

CLI Design Notes
- Command surface:
- Main CLI smell:
- Output contract:
- Completeness signal:
- Ambiguity handling:
- Error behavior:
- Next-action guidance:
- Validation idea:

Use the full shape only when it clarifies the change. For narrow edits, a direct recommendation is better.

Reference

Load references/ai-friendly-cli-design.md when making a broad CLI design change, when tradeoffs are contested, or when you need the full source guide behind these principles.

How to Improve This Skill

If real use reveals a possible improvement, keep the task moving and use report-biaoo-skill-feedback. If unavailable, retain a privacy-safe Biaoo/skills issue draft rather than submitting from this session.