Designing CLIs

Overview

Modern CLIs are conversations between human and machine. Great CLIs feel discoverable, responsive, and forgiving. Poor CLIs leave users guessing, waiting, and frustrated.

Core principle: Every CLI interaction should answer: "What happened? What can I do? What's next?"

When to Use

Building:

• Creating new CLI commands or tools
• Designing output format, error messages, progress indicators
• Planning CLI architecture (flags, subcommands, interaction model)

Improving:

• Enhancing existing CLI user experience
• Adding features to existing commands
• Making CLI "less confusing" or "easier to use"

Reviewing:

• Auditing CLI code for UX issues
• Responding to user complaints about difficulty
• Troubleshooting discoverability problems

Quick Decision Framework

Working On	Read This
New CLI under time pressure	practical-patterns.md (Priority Checklist)
Adding to existing CLI	practical-patterns.md (Working with Existing CLIs)
Fixing "confusing" CLI	practical-patterns.md (CLI UX Audit Checklist)
Command structure, flags	ux-principles.md (Familiarity, Discoverability)
Output formatting	visual-techniques.md (Layout, Spacing, Color)
Error messages, help text	practical-patterns.md (Error Message Patterns)
Overall architecture	ux-principles.md (complete overview)

The Six UX Principles

1. Familiarity - Use known conventions (--help, --version, verb-noun)
2. Discoverability - Guide users (help text, prompts, examples)
3. Feedback - Show what's happening (progress, confirmations, state)
4. Clarity - Structure output (spacing, alignment, hierarchy)
5. Flow - Minimize friction (shortcuts, defaults, scriptability)
6. Forgiveness - Handle errors gracefully (clear messages, suggestions, safety)

See ux-principles.md for detailed guidance and examples.

The Five Visual Techniques

1. Color - Semantic meaning (green=success, red=error, yellow=warning)
2. Spacing - Visual grouping (blank lines, indentation, alignment)
3. Layout - Structured regions (panels, blocks, persistent areas)
4. Symbols - Fast signifiers (✓ ✗ ⚠ →, checkboxes, progress indicators)
5. Structured Feedback - Narrative output (phases, lists, visible progress)

See visual-techniques.md for implementation patterns.

Common Mistakes

❌ Silent operations - No feedback during slow operations ✅ Show progress, confirmations, or at minimum "Working..."

❌ Cryptic errors without guidance - "Error: invalid input" ✅ Explain what's wrong, what's valid, how to fix: "Error: Invalid environment 'production'. Valid: dev, staging, prod"

❌ No --help text - Forces users to read docs or source ✅ Every command supports --help with usage and examples

❌ Wrong exit codes - Always returns 0, breaks scripting ✅ 0 for success, 1 for errors

❌ Color-only information - Inaccessible without color support ✅ Always pair color with text/symbols, support --no-color

❌ Walls of unstructured text - Dense output hard to scan ✅ Use spacing, alignment, hierarchy to structure information

Priority Under Time Pressure

When building CLI urgently, include these first (high impact, low effort):

1. --help flag (2 minutes) - Include usage, examples, common flags
2. Exit codes (1 minute) - 0=success, 1=error, enables CI/CD
3. Clear errors (5 minutes) - What happened + what's valid + how to fix
4. Progress feedback (3 minutes) - Show activity during slow operations

Skip initially (lower priority):

• Color schemes (polish, not function)
• Advanced formatting (tables, columns)
• Multiple output formats (JSON, YAML, etc.)

Cross-References

Detailed guidance:

• practical-patterns.md - Checklists, templates, decision trees
• ux-principles.md - Principles with real-world examples
• visual-techniques.md - Implementation patterns for terminal output
• reading-list.md - Sources and deeper learning

Research materials:

• research/ - Original blog-style documentation and analysis