TUI Design System

Universal design patterns for building exceptional terminal user interfaces. Framework-agnostic — works with Ratatui, Ink, Textual, Bubbletea, or any TUI toolkit.

Core philosophy: TUIs earn their power through spatial consistency, keyboard fluency, and information density that respects human attention. Design for the expert's speed without abandoning the beginner's discoverability.

TUI Design Process

digraph tui_design {
    rankdir=TB;
    "What are you building?" [shape=diamond];
    "Select layout paradigm" [shape=box];
    "Design interaction model" [shape=box];
    "Define visual system" [shape=box];
    "Validate against anti-patterns" [shape=box];
    "Ship it" [shape=doublecircle];

    "What are you building?" -> "Select layout paradigm";
    "Select layout paradigm" -> "Design interaction model";
    "Design interaction model" -> "Define visual system";
    "Define visual system" -> "Validate against anti-patterns";
    "Validate against anti-patterns" -> "Ship it";
}

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1. Layout Paradigm Selector

Choose your primary layout based on what you're building:

App Type	Paradigm	Examples
File manager	Miller Columns	yazi, ranger
Git / DevOps tool	Persistent Multi-Panel	lazygit, lazydocker
System monitor	Widget Dashboard	btop, bottom, oxker
Data browser / K8s	Drill-Down Stack	k9s, diskonaut
SQL / HTTP client	IDE Three-Panel	harlequin, posting
Shell augmentation	Overlay / Popup	atuin, fzf
Log / event viewer	Header + Scrollable List	htop, tig

Persistent Multi-Panel

All panels visible simultaneously. Focus shifts between them. Users build spatial memory — "branches are always top-left."

┌─ Status ──┬─────────── Detail ──────────┐
├─ Files ───┤                              │
│ > file.rs │  diff content here...        │
│   main.rs │                              │
├─ Branches ┤                              │
│ * main    │                              │
│   feat/x  │                              │
├─ Commits ─┤                              │
│ abc1234   │                              │
└───────────┴──────────────────────────────┘
  [q]uit [c]ommit [p]ush [?]help

When to use: Multi-faceted tools where users need simultaneous context (git clients, container managers, monitoring). Key rule: Panels maintain fixed positions across sessions. Never rearrange without user action.

Miller Columns

Three-pane past/present/future navigation. Parent directory (left), current (center), preview (right).

┌── Parent ──┬── Current ──┬── Preview ────────┐
│   ..       │ > config/   │ port: 8080        │
│   src/     │   lib/      │ host: localhost    │
│ > config/  │   main.rs   │ log_level: debug   │
│   tests/   │   mod.rs    │ db_url: postgres://│
└────────────┴─────────────┴───────────────────┘

When to use: Hierarchical data navigation (file systems, tree structures, nested configs). Key rule: Preview pane content adapts to selection type — code gets highlighting, images render, directories show contents.

Drill-Down Stack

Enter descends, Esc ascends. Browser-like navigation through hierarchical data.

When to use: Deep hierarchies where showing all levels simultaneously is impractical (Kubernetes resources, database schemas). Key rule: Always show the current navigation path as a breadcrumb. Provide :resource command-mode for direct jumps.

Widget Dashboard

Self-contained widget panels with independent data. All information visible at once, no navigation required.

┌─── CPU ──────────────┬─── Memory ──────────┐
│ ▁▂▃▅▇█▇▅▃▂▁▂▃▅▇     │ ████████░░ 78%      │
│ core0: 45% core1: 67%│ 12.4G / 16.0G       │
├─── Network ──────────┼─── Disk ────────────┤
│ ▲ 1.2 MB/s  ▼ 340KB/s│ /: 67%  /home: 45%  │
├─── Processes ────────┴─────────────────────┤
│ PID   USER  CPU%  MEM%  CMD                 │
│ 1234  root  23.4  4.5   postgres             │
└─────────────────────────────────────────────┘

When to use: Monitoring, real-time status, system dashboards. Key rule: Each widget is self-contained with its own title. Use braille/block characters for high-density data.

IDE Three-Panel

Sidebar (left), editor/main (center), detail/output (bottom). Tab bar along top.

When to use: Editing-focused tools (SQL clients, HTTP tools, config editors). Key rule: Sidebar toggles with a single key. Center panel supports tabs. Bottom panel can expand to full height.

Overlay / Popup

TUI appears on demand over the shell, disappears after use.

When to use: Shell augmentations (history search, file picker, command palette). Key rule: Configurable height. Return selection to the caller. Never disrupt scrollback.

Header + Scrollable List

Fixed header with meters/stats, scrollable data below, function bar at bottom.

When to use: Single-list tools with metadata (process viewers, log viewers, sorted listings). Key rule: The header creates a natural "overview then detail" reading flow. Sort by the most actionable dimension by default.

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2. Responsive Terminal Design

Terminals resize. Your TUI must handle it gracefully.

Strategy	When
Proportional split	Panels maintain percentage ratios on resize
Priority collapse	Less important panels hide first below minimum width
Stacking	Panels collapse to title-only bars, active one expands (zellij pattern)
Breakpoint modes	Switch layout entirely below a threshold (e.g., multi-panel → single panel)
Minimum size gate	Display "terminal too small" if below usable minimum

Rules:

• Define a minimum terminal size (typically 80x24). Below that, show a resize message.
• Never crash on resize. Handle SIGWINCH gracefully.
• Use constraint-based layouts (percentages, min/max, ratios) — not absolute positions.
• Test at 80x24, 120x40, and 200x60 to verify scaling.

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3. Interaction Model

Navigation Style Selector

App Complexity	Recommended Model
Single-purpose, <20 actions	Direct keybinding (every key = action)
Multi-view, complex	Vim-style modes + contextual footer
IDE-like, many features	Command palette + tabs + vim motions
Data browser	Drill-down + fuzzy search + : command mode

Keyboard Design Layers

Design keybindings in four progressive layers:

Layer	Keys	Audience	Always show?
L0: Universal	Arrow keys, Enter, Esc, q	Everyone	Yes (footer)
L1: Vim motions	hjkl, /, ?, :, gg, G	Intermediate	Yes (footer)
L2: Actions	Single mnemonics: d(elete), c(ommit), p(ush)	Regular users	On ? help
L3: Power	Composed commands, macros, custom bindings	Power users	Docs only

Keybinding conventions (lingua franca):

• j/k — move down/up
• h/l — move left/right (or collapse/expand)
• / — search
• ? — help overlay
• : — command mode
• q — quit (or Esc to go back one level)
• Enter — select / confirm / drill in
• Tab — switch focus between panels
• Space — toggle selection
• g/G — jump to top/bottom

Never bind: Ctrl+C (interrupt), Ctrl+Z (suspend), Ctrl+\ (quit signal). These belong to the terminal.

Focus Management

• Only one widget receives keyboard input at a time
• Tab cycles focus forward, Shift+Tab backward
• Focus indicator: highlighted border, color change, or cursor presence
• Unfocused panels: dimmed or thinner borders
• Modal dialogs create focus traps — background receives no events
• Nested focus: outer container routes events to focused child

Search & Filtering

The universal pattern: press /, type query, results filter live.

• n/N — next/previous match
• Esc — dismiss search
• Fuzzy matching by default, ' prefix for exact match
• Highlight matched characters in results
• Preview pane updates for highlighted result

Help System — Three Tiers

Tier	Trigger	Content	Audience
Always visible	Footer bar	3-5 essential shortcuts	Everyone
On demand	? key	Full keybinding overlay for current context	Regular users
Documentation	--help, man page	Complete reference	Power users

Footer format: [q]uit [/]search [?]help [Tab]focus [Enter]select

Context-sensitive footers update based on the active panel or mode. Show only what's actionable right now.

Dialogs & Confirmation

Action Severity	Pattern
Reversible	Just do it, show brief confirmation in status bar
Moderate (delete file)	Inline "Press y to confirm"
Severe (drop database)	Modal dialog requiring resource name input
Irreversible batch	--dry-run flag + explicit confirmation

• Modal overlays: render popup on top of dimmed/blurred background
• Toast notifications: auto-dismiss after 3-5 seconds, no interaction required
• Status bar messages: vim-style one-liner feedback, auto-fade

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4. Color Design System

Terminal Color Tiers

Design for graceful degradation across all three tiers:

Tier	Escape Sequence	Colors	Strategy
16 ANSI	\033[31m	16 (relative)	Foundation. Terminal theme controls appearance.
256 Color	\033[38;5;{n}m	256 (16 relative + 240 fixed)	Extended palette. Fixed colors may clash with themes.
True Color	\033[38;2;{r};{g};{b}m	16.7M (absolute)	Full control. Requires COLORTERM=truecolor.

Detection hierarchy:

1. $COLORTERM = truecolor or 24bit → true color
2. $TERM contains 256color → 256 colors
3. $NO_COLOR is set → disable all color
4. Default → 16 ANSI colors

Golden rule: Your TUI must be usable in 16-color mode. True color enhances — it never creates the hierarchy.

Semantic Color Slots

Define colors by function, not appearance. Map semantics to actual colors through your theme:

Slot	Purpose	Typical Dark Theme
fg.default	Body text	Off-white (#c0caf5)
fg.muted	Secondary text, metadata	Gray (#565f89)
fg.emphasis	Headers, focused items	Bright white (#e0e0e0)
bg.base	Primary background	Near-black (#1a1b26)
bg.surface	Panel/widget backgrounds	Slightly lighter (#24283b)
bg.overlay	Popup/dialog backgrounds	Lighter still (#414868)
bg.selection	Selected item highlight	Distinct (#364a82)
accent.primary	Interactive elements, focus	Brand color (#7aa2f7)
accent.secondary	Supporting interactions	Complementary (#bb9af7)
status.error	Errors, deletions	Red (#f7768e)
status.warning	Warnings, caution	Yellow (#e0af68)
status.success	Success, additions	Green (#9ece6a)
status.info	Informational	Cyan (#7dcfff)

Never hardcode hex values in widget code. Always reference semantic slots.

Visual Hierarchy Techniques

Color is one tool among several. Use them in combination:

Technique	Effect	Use For
Bold (SGR 1)	Increases visual weight	Headers, labels, active items
Dim (SGR 2)	Decreases visual weight	Metadata, timestamps, secondary info
Italic (SGR 3)	Semantic distinction	Comments, types, annotations
Underline (SGR 4)	Links, actionable items	Clickable elements, URLs
Reverse (SGR 7)	Swaps fg/bg	Selection highlight (always works!)
Strikethrough (SGR 9)	Negation	Deleted items, deprecated features

Hierarchy recipe: 80% of content in fg.default. Headers in bold + fg.emphasis. Metadata in dim + fg.muted. Status in their semantic colors. Accents for interactive elements only.

Background Layering

Create depth without borders by layering background lightness:

bg.base (darkest) → bg.surface → bg.overlay (lightest)

Each step ~5-8% lighter in dark themes. The eye perceives depth from the contrast gradient. This reduces the need for box-drawing borders while maintaining clear visual zones.

Theme Architecture

Follow the Base16 pattern: define 16 named color slots, map them semantically:

• 8 monotones (base00-base07): background/foreground gradient
• 8 accents (base08-base0F): syntax/semantic colors

Ship a dark theme by default. Detect light/dark terminal via OSC escape query or terminal-light crate. Provide at least one light variant. Respect NO_COLOR.

Accessibility Requirements

• WCAG AA contrast: 4.5:1 ratio for body text, 3:1 for large text/UI elements
• Never use color alone: Pair with symbols (checkmark, X, triangle), text labels, position, or typography
• Color blindness safe pairs: blue+orange, blue+yellow, black+white. Avoid relying on red vs green.
• Test: monochrome mode, color blindness simulator, 3+ terminal emulators, light and dark themes

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5. Data Visualization

Character-Resolution Building Blocks

Element	Characters	Resolution	Use For
Full blocks	█▉▊▋▌▍▎▏	8 steps/cell	Progress bars, bar charts
Shade blocks	░▒▓█	4 densities	Heatmaps, density plots
Braille	⠁⠂⠃...⣿ (U+2800-U+28FF)	2x4 dots/cell	High-res line graphs, scatter plots
Sparkline	▁▂▃▄▅▆▇█	8 heights	Inline mini-charts

Common Widgets

Widget	Pattern	Tips
Progress bar	[████████░░░░] 67%	Show percentage + ETA. Color gradient green→yellow→red by urgency.
Sparkline	▁▂▃▅▇█▇▅▃▂	Perfect for inline time-series in headers/status bars.
Gauge	CPU [██████████░░] 83%	Label + bar + value. Color by threshold.
Table	Sortable columns, zebra stripes	Align numbers right, text left. Truncate with ….
Tree	├── , └── , │ guides	Indent 2-4 chars per level. Expand/collapse with Enter.
Diff	Green + lines, red - lines	Word-level highlighting within changed lines elevates quality.
Log	Colored level, timestamp, message	TRACE=dim, DEBUG=cyan, INFO=default, WARN=yellow, ERROR=red, FATAL=red+bold.

Spinner Selection

Context	Spinner	Interval
Default / modern	Braille dots ⠋⠙⠹⠸⠼⠴⠦⠧⠇⠏	80ms
Minimal	Line -|/	130ms
Heavy processing	Blocks ▖▘▝▗	100ms
Fun / branded	Custom frames	70-100ms

Use spinners for indeterminate operations. Progress bars for determinate. Show spinners only after 200ms delay to avoid flash on fast operations.

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6. Animation & Motion

Flicker-Free Rendering Stack

Three layers, all required for smooth TU