Design CLI Output

Design CLI Output

Consistent, multi-level terminal output for a command-line tool.

When Use

• Build new reporter module for CLI tool
• Add warm or narrative output alongside transactional output
• Standardize output format across many commands
• Design JSON machine output parallel to human output
• Pick colors, glyphs, verbosity levels for new terminal tool

Inputs

• Required: CLI tool name + primary audience (devs, operators, end users)
• Required: Commands that need output formatting
• Optional: Ceremony/narrative output variant wanted?
• Optional: Brand constraints (color palette, tone)

Steps

Step 1: Set Color Palette

Use chalk. Make named palette object.

Load chalk behind no-color fallback. Fallback must stand in for every call shape palette uses — more than passing strings through:

// A factory returns a *function*; a direct style returns a string. Enumerate
// this list against the installed chalk, not from memory — chalk 6 added the
// three underline* variants, and a list that omits them is wrong for those names.
const FACTORIES = new Set(['ansi256', 'bgAnsi256', 'bgHex', 'bgRgb', 'hex',
  'rgb', 'underlineAnsi256', 'underlineHex', 'underlineRgb']);

function makeChalkStub() {
  return new Proxy((text) => text, {
    get(target, prop) {
      if (prop === 'then') return undefined;   // must not be a thenable
      if (prop === 'level') return 0;          // no color support, truthfully
      if (typeof prop === 'symbol') return Reflect.get(target, prop);
      return FACTORIES.has(prop) ? () => makeChalkStub() : makeChalkStub();
    },
  });
}

let chalk;
try { chalk = (await import('chalk')).default; }
catch { chalk = makeChalkStub(); }

Four invariants. Shorter stub gets each one wrong:

1. Proxy target callable — (text) => text, not {}. Chaining (chalk.bold.cyan('x')) needs every hop both indexable + callable.
2. Factories return function. new Proxy({}, { get: () => (s) => s }) satisfies direct styles, breaks factories: chalk.hex('#FF6B35') is then string '#FF6B35', and calling it throws TypeError: ... is not a function. Palettes built at module load, so that fallback takes tool down at import time — exactly where degrading to plain text was point.
3. then is undefined. Stub answering every property with function makes await chalk hang forever: runtime calls .then, waits for callback nobody invokes. Node reports Detected unsettled top-level await, exits 13.
4. level is number. Capability gates read chalk.level >= 1; truthy stub opens them with no color support behind.

Build palette from whichever object survived that import.

Standard palette (transactional output):

// Status colors
const ok = chalk.green;       // success
const fail = chalk.red;       // errors
const warn = chalk.yellow;    // warnings
const info = chalk.cyan;      // identifiers, names
const dim = chalk.dim;        // secondary info, paths
const bold = chalk.bold;      // headers

Warm palette (ceremony/narrative output):

const C = {
  flame: chalk.hex('#FF6B35'),   // active elements, fire
  amber: chalk.hex('#FFB347'),   // arriving items, warm highlights
  spark: chalk.hex('#FFF4E0'),   // individual items (sparks/skills)
  ember: chalk.hex('#8B4513'),   // cold/dormant states
  warm:  chalk.hex('#D4A574'),   // neutral warm text
  dim:   chalk.dim,              // background, secondary
  fail:  chalk.red,              // errors stay red (honest)
};

Palette rules:

• Always provide no-color fallback, and check it against call shapes palette actually uses — warm palette above almost all factories
• Use hex colors for custom palettes (chalk.hex('#FF6B35'))
• Keep fail/error red no matter the theme
• Name palette by semantic role, not visual
• Share one stub across modules, not rebuild at each import site — else same defect must be found + fixed in every copy

Got: Palette object. Named entries. Fallback executed, not merely written.

If fail: Exercise fallback path directly; palette is wrong place to discover it broken. With stub in scope:

console.assert(chalk.dim('x') === 'x');            // direct style
console.assert(chalk.hex('#fff')('x') === 'x');    // factory — the usual defect
console.assert(chalk.bold.cyan('x') === 'x');      // chain
console.assert(chalk.level === 0);                 // capability gate stays shut
await chalk;                                       // must not hang

NO_COLOR=1 does not cover this. It exercises working chalk that chooses not to emit escapes; fallback exercises chalk that failed to import. Two paths share no code. See Extended Examples for annotated production stub, reproduction of defect, runnable version of checks above.

Step 2: Pick Status Indicators

Unicode glyphs or ASCII chars for status.

ASCII (max compat):

+  created/installed (green)
-  removed/deleted (red)
=  skipped/unchanged (dim)
!  error/warning (red)

Unicode (richer, needs UTF-8 terminal):

✦  item/skill/practice (spark)
◉  active/burning state
◎  cooling/embers state
○  cold/dormant state
◌  available/not installed
✗  failed item
✓  success (use sparingly — not all terminals render it well)

Rules:

• ASCII for CI or piped contexts
• Unicode for interactive terminal users
• Offer both via --ascii flag or NO_COLOR detection
• Test glyphs in: macOS Terminal, Windows Terminal, VS Code terminal, SSH

Got: Glyph set communicates status at a glance. No color needed.

If fail: Glyph renders as ? or box? Swap for ASCII. +/-/=/! works everywhere.

Step 3: Design Verbosity Levels

Every command supports 4 output levels:

Pattern:

function output(data, options) {
  if (options.json) {
    console.log(JSON.stringify(data, null, 2));
    return;
  }
  if (options.quiet) {
    for (const item of data.items) {
      const icon = item.ok ? '+' : '!';
      console.log(`${icon} ${item.id}`);
    }
    return;
  }
  // Default (or verbose) human output
  printFormatted(data, { verbose: options.verbose });
}

JSON rules:

• Always valid JSON (no mixing with human text)
• Include all data human output shows, plus machine fields
• Consistent key names across commands
• Exit 0 = success, 1 = err (any output mode)

Got: Four clear output levels. Consistent across commands.

If fail: Verbose too noisy? Make opt-in (--ceremonial) not graduated level.

Step 4: Set Voice Rules

Tone + style all output follows. Stops inconsistency.

Example voice rules (campfire reporter):

1. Present tense, active voice: "mystic arrives" not "mystic has been installed"
2. No exclamation marks: Quiet confidence. Tool doesn't shout.
3. Metaphor replaces jargon: "practices" not "dependencies" (ceremony mode only)
4. Failures honest, not catastrophic: "A spark was lost" not "ERROR: installation failed with exit code 1"
5. Closing line shows state: Every op ends with status summary
6. No emoji: Unicode glyphs carry visual weight without decoration
7. Every word carries info: Word adds no understanding? Remove.

Voice rules for standard (non-ceremony) output:

• Concise, factual lines
• Status icon + item ID + context
• Summary line with counts
• Errors suggest fix

Got: Written set of 3-7 voice rules. Output funcs must follow.

If fail: Rules feel arbitrary? Test: write output with + without each rule. Removing rule doesn't change quality? Rule not needed.

Step 5: Build Reporter Functions

Organize output into reporter module. Focused functions.

// reporter.js — standard output
export function printResults(results) { ... }
export function printItemTable(items) { ... }
export function printDetections(detections) { ... }
export function printAudit(auditResults) { ... }
export function printDryRun() { ... }
export function warn(msg) { ... }
export function error(msg) { ... }
export { chalk };

Each function same structure:

1. Handle empty/null input
2. Compute layout (col widths, padding)
3. Output with palette colors
4. Summary line at bottom

Ceremony output? Separate module:

// campfire-reporter.js — warm narrative output
export function printArrival({ teamId, agents, results, ceremonial }) { ... }
export function printScatter({ teamId, agents, results }) { ... }
export function printTend(fires) { ... }
export function printCampfireList({ teams, state, reg }) { ... }
export function printFireSummary({ team, fireData, reg }) { ... }
export function printJson(data) { ... }

Got: Reporter functions independently usable. Each handles own formatting, no caller state dep.

If fail: Function > ~50 lines? Extract helpers. Reporter must be reviewable alone.

Step 6: Test Output Across Environments

Check output renders right in different contexts:

# With colors (interactive terminal)
node cli/index.js list --domains

# Without colors (piped)
node cli/index.js list --domains | cat

# With NO_COLOR environment variable
NO_COLOR=1 node cli/index.js list --domains

# JSON mode (parseable)
node cli/index.js campfire --json | jq .

# In CI (typically no TTY)
CI=true node cli/index.js audit

# The no-color fallback. A failed import cannot be provoked with an env var, so
# assert on the stub itself in the suite rather than reaching it through the CLI.
# Pass a glob, not a directory: `node --test <dir>` stopped expanding at Node 22.
node --test 'cli/test/*.test.js'

Check:

• Colors display right in interactive mode
• No ANSI escape codes leak into piped/redirected output
• JSON valid (pipe to jq .)
• Unicode glyphs render in target terminals
• Column alignment holds with varying content widths
• No-color fallback answers every call shape palette uses, asserted in suite, not demonstrated once by hand

Got: Output correct in all 6 contexts.

If fail: ANSI codes leak? Ensure chalk respects NO_COLOR. Unicode breaks? Provide ASCII fallback mode. Note green suite says nothing about color either way: test runners pipe stdout, which puts chalk.level at 0, so colored + uncolored output byte-identical — assertions hold with color entirely broken. Proving color works needs FORCE_COLOR=3 + assertion on escape sequence.

Checks

• Color palette has no-color fallback, and fallback has been run: direct style, factory, chain, level === 0, await all checked
• Status indicators work in both color + no-color modes
• All 4 verbosity levels produce useful output
• JSON output valid, parseable by jq
• Voice rules documented + followed
• Reporter funcs handle empty/null input
• Output tested in: terminal, piped, NO_COLOR, CI

Pitfalls

• No-color fallback that only handles direct styles: new Proxy({}, { get: () => (s) => s }) reads complete and does cover chalk.dim + chalk.red, but every factory then returns string caller immediately tries to call. Palettes built at module load, so TypeError lands at import time — fallback fails hardest in the one case it exists for. Step 1 lists four invariants stub must satisfy.
• Mixing human text with JSON: In --json mode, only valid JSON. One stray line ("DRY RUN") breaks JSON parsers. If must show both, separate clearly or suppress human text in JSON mode.
• Hardcoded column widths: Content length varies. Use Math.max(...items.map(i => i.id.length)) for dynamic padding.
• Color without meaning: Color only way to tell success from failure? Colorblind users + piped output lose info. Always pair color with text indicator (+, OK, ERR).
• Ceremony in wrong context: Warm narrative output fits interactive terminal. In CI, scripts, --quiet mode = noise. Gate ceremony behind explicit flags.
• Forgetting summary line: Users scan last line first. Every op ends with one-line summary (counts of success/failure/skipped).

See Also

• scaffold-cli-command — commands that use this output
• test-cli-application — testing output matches expectations
• build-cli-plugin — plugins report results through this output system