Design CLI Output

Design CLI Output

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

When to Use

• Building a new reporter module for a CLI tool
• Adding warm or narrative output alongside standard transactional output
• Standardizing output format across multiple commands
• Designing JSON machine output parallel to human-readable output
• Choosing colors, glyphs, and verbosity levels for a new terminal tool

Inputs

• Required: CLI tool name and primary audience (developers, operators, end users)
• Required: Commands that need output formatting
• Optional: Whether a "ceremony" or narrative output variant is desired
• Optional: Branding constraints (color palette, tone)

Procedure

Step 1: Define the Color Palette

Use chalk to create a named palette object.

Load chalk behind a no-color fallback. The fallback has to stand in for every call shape the palette uses, which is 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, each of which a shorter stub gets wrong:

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

Build the 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 design rules:

• Always provide a no-color fallback, and check it against the call shapes the palette actually uses — the warm palette above is almost entirely factories
• Use hex colors for custom palettes (chalk.hex('#FF6B35'))
• Keep the fail/error color red regardless of palette theme
• Name palette entries by semantic role, not visual appearance
• Share one stub across modules instead of rebuilding it at each import site, or the same defect has to be found and fixed in every copy

Expected: A palette object with named entries, and a fallback that has been executed rather than merely written.

On failure: Exercise the fallback path directly; the palette is the wrong place to discover it is broken. With the 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 a working chalk that chooses not to emit escapes; the fallback exercises a chalk that failed to import. The two paths share no code. See Extended Examples for the annotated production stub, a reproduction of the defect, and a runnable version of the checks above.

Step 2: Choose Status Indicators

Select Unicode glyphs or ASCII characters for status communication:

ASCII (maximum compatibility):

+  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)

Selection criteria:

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

Expected: A glyph set that communicates status at a glance without relying on color alone.

On failure: If a glyph renders as ? or a box in testing, replace with the ASCII equivalent. The +/-/=/! set works everywhere.

Step 3: Design Verbosity Levels

Every command should support four output levels:

Implementation 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 output rules:

• Always valid JSON (no mixing with human text)
• Include all data the human output shows, plus machine-useful fields
• Use consistent key naming across commands
• Exit code 0 for success, 1 for errors (regardless of output mode)

Expected: Four clear output levels with consistent behavior across commands.

On failure: If verbose mode is too noisy, make it opt-in (--ceremonial) rather than a graduated verbosity level.

Step 4: Establish Voice Rules

Define the tone and style that all output functions follow. This prevents inconsistency across commands.

Example voice rules (from the campfire reporter):

1. Present tense, active voice: "mystic arrives" not "mystic has been installed"
2. No exclamation marks: Quiet confidence. The tool doesn't shout.
3. Metaphor replaces jargon: "practices" not "dependencies" (only for ceremony mode)
4. Failures are honest, not catastrophic: "A spark was lost" not "ERROR: installation failed with exit code 1"
5. Closing line reflects state: Every operation ends with a status summary
6. No emoji: Unicode glyphs carry visual weight without being decorative
7. Every word carries information: If a word doesn't add understanding, remove it

Voice rules for standard (non-ceremony) output:

• Concise, factual lines
• Status icon + item ID + context
• Summary line with counts
• Error messages suggest corrective actions

Expected: A written set of 3-7 voice rules that output functions must follow.

On failure: If rules feel arbitrary, test them: write the same output with and without each rule. If removing a rule doesn't change the output quality, the rule isn't needed.

Step 5: Implement Reporter Functions

Organize output into a reporter module with 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 follows the same structure:

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

For ceremony output, create a 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) { ... }

Expected: Reporter functions that are independently usable — each handles its own formatting without depending on caller state.

On failure: If functions grow beyond ~50 lines, extract helpers. A reporter function should be easy to review in isolation.

Step 6: Test Output Across Environments

Verify output renders correctly 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 for:

• Colors display correctly in interactive mode
• No ANSI escape codes leak into piped/redirected output
• JSON is valid (pipe to jq . to verify)
• Unicode glyphs render in the target terminals
• Column alignment holds with varying content widths
• The no-color fallback answers every call shape the palette uses, asserted in the suite rather than demonstrated once by hand

Expected: Output is correct in all six contexts.

On failure: If ANSI codes leak, ensure chalk respects NO_COLOR. If Unicode breaks, provide an ASCII fallback mode. Note that a green suite says nothing about color either way: test runners pipe stdout, which puts chalk.level at 0, so colored and uncolored output are byte-identical and the assertions hold with color entirely broken. Proving color works needs FORCE_COLOR=3 and an assertion on an escape sequence.

Validation

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

Common Pitfalls

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

Related Skills

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