CLI Design

CLI Design

Design a command-line tool's interface before implementation: human-first, script-friendly, Linux-only. Output is a compact spec the user or an agent can implement directly. Rubric source: clig.dev (rebuilt as references/clig-checklist.md).

Workflow

Phase 1: SCOPE

Lock the interface with the minimum questions. Proceed with the conventions in Phase 2 when the user is unsure.

• Command name and one-sentence purpose.
• Primary user: humans, scripts, or both.
• Input sources: args vs stdin; files vs URLs. Secrets travel via file or stdin, because flags leak through ps and shell history.
• Output contract: human text, --json, --plain, exit codes.
• Interactivity: prompts allowed? --no-input needed? confirmation for destructive ops?
• Config model: flags, env, config file; precedence.

Gate: name, purpose, and I/O contract are known. Proceed only when gate passes.

Phase 2: DESIGN

Load references/clig-checklist.md and apply it as the default rubric. For each section, pick the convention and record it in the spec. Diverge from a convention only deliberately, and document the divergence in the spec — interfaces are contracts, and surprising contracts break scripts.

Phase 3: DELIVER

Produce the spec from this skeleton. Drop a section only when it genuinely has no content; fill every other section.

1. Name and one-liner: command name plus a single sentence of purpose
2. Usage line: the synopsis as --help will print it, global flags and subcommand slot included
3. Subcommands: purpose of each, whether it mutates state, whether re-running it is safe
4. Args/flags table: columns for name, type, default, required?, example
5. I/O contract: primary data and machine-readable output on stdout; everything else (errors, progress, logs) on stderr
6. Exit codes: map each failure mode to a code — success 0, failure 1, bad usage 2; mint extra codes only for cases scripts must distinguish
7. Safety: --dry-run, confirmation rules, --force, --no-input
8. Env/config: env vars; config file path; precedence order with flags highest, then env, project config, user config, system
9. Examples: enough invocations to cover the common flows; show at least one pipeline or stdin use

Gate: every flag used in the examples appears in the flags table, and every failure mode shown maps to an exit code.

Constraints

• Stay at spec altitude: when the request is "design the interface," deliver the spec and stop. Implementation is a separate task.
• Keep the spec language-agnostic. Recommend a parsing library only when asked.
• Target Linux. Skip Windows/macOS path, signal, and packaging concerns.

Error handling

Request mixes design and implementation

Cause: user says "design and build." Solution: deliver the spec first, get confirmation, then implement against it.

Spec balloons past one page

Cause: subcommand sprawl or speculative flags. Solution: cut flags that lack a named user need; defaults should serve most users without aliases.