TUI and CLI Patterns

Actionable terminal interface patterns for requirements gathering and design review. Use when target is CLI tool or interactive terminal application.

CLI Argument Design

Command Structure

Follow program subcommand [flags] [arguments] (e.g., git commit -m "message").

Flags and Options

• Both short (-h) and long (--help) for common flags
• Reserve single-letter flags for frequently used options
• Standard flags always: --help, --version, --verbose/--quiet, --no-color
• Never accept secrets via flags (use files, stdin, or env vars)
• Make flag order independent

Subcommands

• Verbs for actions: create, delete, list, show, update
• Nouns for targets: user, project, config
• Pick one pattern (tool resource action or tool action resource) consistently
• Provide shell completion scripts for discoverability

Argument Design Principles

Required arguments are positional; optional use flags. Accept stdin for piping. Support glob patterns for file arguments. Provide --dry-run for destructive/complex operations.

Interactive TUI Patterns

Framework Architectures

Framework	Language	Architecture	Best For
Bubble Tea	Go	Elm (Model-Update-View)	Full TUI apps with complex state
Rich	Python	Declarative rendering	Beautiful output, progress, tables
Ink	JavaScript	React component model	Teams with React experience
Textual	Python	CSS-like styling, widgets	Dashboard-style applications
Ratatui	Rust	Immediate-mode rendering	High-performance terminal apps

Key Architectural Pattern (Elm Architecture)

• Model: Application state (single data structure)
• Update: Pure function taking model + message, returns new model
• View: Pure function rendering model to string

Unidirectional data flow makes TUI state predictable and testable.

Interactive Selection Patterns

Arrow keys to navigate, Enter to select. Type-ahead filtering for long lists. Multi-select with space bar, confirm with Enter. Show selected count with clear visual indicator. Support Esc to cancel.

Color and Formatting

Color Conventions

Red: errors, failures, deletions | Yellow/amber: warnings, attention | Green: success, confirmations, additions | Blue/cyan: information, links, highlights | Dim/gray: secondary info, metadata

Color Rules

• Never use color as only way to convey information (accessibility)
• Respect NO_COLOR environment variable (no-color.org)
• Detect TTY: disable color when piped or redirected
• Test with color-blindness simulators (protanopia, deuteranopia)

Formatting Patterns

Bold for emphasis and headings | Tables for structured data | Indentation for hierarchy | Horizontal rules for section breaks | Unicode box-drawing for visual structure (provide ASCII fallback)

Error Message Design

Every CLI error answers three questions:

1. What happened? Clear, jargon-free description
2. Why? The cause or context
3. What to do? Concrete next step

Good Example

Error: Could not connect to database at localhost:5432

  The connection was refused. The database server may not be
  running or is not accepting connections on this port.

  Try:
    1. Check if PostgreSQL is running:  pg_isready -h localhost -p 5432
    2. Start the server:                sudo systemctl start postgresql
    3. Verify the port in config:       cat ~/.config/myapp/database.yaml

  Documentation: https://docs.myapp.com/troubleshooting/database

Bad Example

Error: ECONNREFUSED

Error Guidelines

• Never blame user ("You entered invalid..." becomes "The value ... is not valid because...")
• Suggest most likely correction (did-you-mean for typos)
• Exit codes consistent: 0=success, 1=general error, 2=usage error
• Log verbose diagnostics to file, not stderr by default

Help Text Design

--help Output Structure

tool-name - One-line description

USAGE
  tool-name <command> [flags]

COMMANDS
  create    Create a new resource
  list      List existing resources
  delete    Remove a resource

FLAGS
  -h, --help       Show this help message
  -v, --version    Show version information
  -q, --quiet      Suppress non-error output

EXAMPLES
  # Create a new project
  tool-name create my-project --template=web

  # List all projects
  tool-name list --format=table

LEARN MORE
  Documentation:  https://docs.tool-name.com
  Report issues:  https://github.com/org/tool-name/issues

Help Text Principles

Lead with examples (users scan for examples first). Show common commands/flags first. One line per description. Link to detailed docs. Support both tool help <cmd> and tool <cmd> --help.

Output Design

Human-Readable (Default)

Detect TTY: terminal gets colors, tables, progress bars. Disable animations/spinners in non-TTY mode. Use structured formatting (headers, indentation, alignment).

Machine-Parseable Alternatives

• --json for structured output (most important machine format)
• --plain or --tsv for tabular data compatible with grep, awk, cut
• --quiet for scripts needing only exit code

Output Contract

Once --json schema published, treat as API contract. Breaking changes require major version bump or --output-version flag.

Progress and Responsiveness

• Respond within 100ms: output something immediately, especially before network calls
• Spinner for operations 1-5 seconds
• Progress bar with percentage for operations >5 seconds
• Multi-step: [3/7] Installing dependencies...
• Make operations idempotent where possible (safe to re-run after interruption)
• Handle Ctrl+C cleanly with proper cleanup

CLI/TUI Anti-Patterns

Anti-Pattern	Alternative
Wall of unformatted text	Structured output with headers, tables, color
Raw exception stack traces	Caught errors rewritten in human language
No --help or misleading help	Comprehensive, example-led help text
Requiring interactive input in CI/CD	Detect non-TTY and accept flags/env vars
Breaking JSON output between versions	Treat machine output as versioned API contract
Secrets accepted via flags	Use files, stdin, or environment variables
Color as only information channel	Pair color with text labels or symbols

CLI/TUI Review Checklist

Discoverability

• --help produces useful, example-led output
• Subcommands use consistent verb/noun patterns
• Shell completion scripts available
• Did-you-mean suggestions for typos

Output

• Default output is human-readable with color in TTY
• --json flag available for machine consumption
• Color never only way to convey information
• NO_COLOR environment variable respected
• Animations disabled in non-TTY mode

Error Handling

• Errors answer: what happened, why, what to do
• No raw stack traces in user-facing output
• Exit codes consistent (0=success, 1=error, 2=usage)
• Suggestions for common mistakes

Responsiveness

• First output within 100ms
• Spinner for 1-5 second operations
• Progress bar for longer operations
• Ctrl+C handled with clean cleanup

Configuration

• Precedence: flags > env vars > project config > user config > defaults
• Secrets never via flags
• Sensible defaults for all optional config