visual-explainer

name	visual-explainer
description	Generate beautiful, self-contained HTML pages that visually explain systems, code changes, plans, and data. Use when the user asks for a diagram, architecture overview, diff review, plan review, project recap, comparison table, or any visual explanation of technical concepts. Also use proactively when you are about to render a complex ASCII table (4+ rows or 3+ columns) — present it as a styled HTML page instead.
license	MIT
compatibility	Requires a browser to view generated HTML files. Optional surf-cli for AI image generation.
metadata	{"author":"nicobailon","version":"0.2.0"}

Visual Explainer

Generate self-contained HTML files for technical diagrams, visualizations, and data tables. Always open the result in the browser. Never fall back to ASCII art when this skill is loaded.

Proactive table rendering. When you're about to present tabular data as an ASCII box-drawing table in the terminal (comparisons, audits, feature matrices, status reports, any structured rows/columns), generate an HTML page instead. The threshold: if the table has 4+ rows or 3+ columns, it belongs in the browser. Don't wait for the user to ask — render it as HTML automatically and tell them the file path. You can still include a brief text summary in the chat, but the table itself should be the HTML page.

Workflow

1. Think (5 seconds, not 5 minutes)

Before writing HTML, commit to a direction. Don't default to "dark theme with blue accents" every time.

Who is looking? A developer understanding a system? A PM seeing the big picture? A team reviewing a proposal? This shapes information density and visual complexity.

What type of diagram? Architecture, flowchart, sequence, data flow, schema/ER, state machine, mind map, data table, timeline, or dashboard. Each has distinct layout needs and rendering approaches (see Diagram Types below).

What aesthetic? Pick one and commit. The constrained aesthetics (Blueprint, Editorial, Paper/ink) are safer — they have specific requirements that prevent generic output. The flexible ones (IDE-inspired) require more discipline.

Constrained aesthetics (prefer these):

• Blueprint (technical drawing feel, subtle grid background, deep slate/blue palette, monospace labels, precise borders) — see websocket-implementation-plan.html for reference
• Editorial (serif headlines like Instrument Serif or Crimson Pro, generous whitespace, muted earth tones or deep navy + gold)
• Paper/ink (warm cream #faf7f5 background, terracotta/sage accents, informal feel)
• Monochrome terminal (green/amber on near-black, monospace everything, CRT glow optional)

Flexible aesthetics (use with caution):

• IDE-inspired (borrow a real, named color scheme: Dracula, Nord, Catppuccin Mocha/Latte, Solarized Dark/Light, Gruvbox, One Dark, Rosé Pine) — commit to the actual palette, don't approximate
• Data-dense (small type, tight spacing, maximum information, muted colors)

Explicitly forbidden:

• Neon dashboard (cyan + magenta + purple on dark) — always produces AI slop
• Gradient mesh (pink/purple/cyan blobs) — too generic
• Any combination of Inter font + violet/indigo accents + gradient text

Vary the choice each time. If the last diagram was dark and technical, make the next one light and editorial. The swap test: if you replaced your styling with a generic dark theme and nobody would notice the difference, you haven't designed anything.

2. Structure

Read the reference template before generating. Don't memorize it — read it each time to absorb the patterns.

• For text-heavy architecture overviews (card content matters more than topology): read ./templates/architecture.html
• For flowcharts, sequence diagrams, ER, state machines, mind maps: read ./templates/mermaid-flowchart.html
• For data tables, comparisons, audits, feature matrices: read ./templates/data-table.html
• For slide deck presentations (when --slides flag is present or /generate-slides is invoked): read ./templates/slide-deck.html and ./references/slide-patterns.md

For CSS/layout patterns and SVG connectors, read ./references/css-patterns.md.

For pages with 4+ sections (reviews, recaps, dashboards), also read ./references/responsive-nav.md for section navigation with sticky sidebar TOC on desktop and horizontal scrollable bar on mobile.

Choosing a rendering approach:

Diagram type	Approach	Why
Architecture (text-heavy)	CSS Grid cards + flow arrows	Rich card content (descriptions, code, tool lists) needs CSS control
Architecture (topology-focused)	Mermaid	Visible connections between components need automatic edge routing
Flowchart / pipeline	Mermaid	Automatic node positioning and edge routing
Sequence diagram	Mermaid	Lifelines, messages, and activation boxes need automatic layout
Data flow	Mermaid with edge labels	Connections and data descriptions need automatic edge routing
ER / schema diagram	Mermaid	Relationship lines between many entities need auto-routing
State machine	Mermaid	State transitions with labeled edges need automatic layout
Mind map	Mermaid	Hierarchical branching needs automatic positioning
Data table	HTML <table>	Semantic markup, accessibility, copy-paste behavior
Timeline	CSS (central line + cards)	Simple linear layout doesn't need a layout engine
Dashboard	CSS Grid + Chart.js	Card grid with embedded charts

Mermaid theming: Always use theme: 'base' with custom themeVariables so colors match your page palette. Use layout: 'elk' for complex graphs (requires the @mermaid-js/layout-elk package — see ./references/libraries.md for the CDN import). Override Mermaid's SVG classes with CSS for pixel-perfect control. See ./references/libraries.md for full theming guide.

Mermaid zoom controls: Always add zoom controls (+/−/reset buttons) to every .mermaid-wrap container. Complex diagrams render at small sizes and need zoom to be readable. Include Ctrl/Cmd+scroll zoom on the container. See the zoom controls pattern in ./references/css-patterns.md and the reference template at ./templates/mermaid-flowchart.html.

Mermaid CSS class collision constraint: Never define .node as a page-level CSS class. Mermaid.js uses .node internally on SVG <g> elements with transform: translate(x, y) for positioning. Page-level .node styles (hover transforms, box-shadows) leak into diagrams and break layout. Use the namespaced .ve-card class for card components instead. The only safe way to style Mermaid's .node is scoped under .mermaid (e.g., .mermaid .node rect).

AI-generated illustrations (optional). If surf-cli is available, you can generate images via Gemini and embed them in the page for creative, illustrative, explanatory, educational, or decorative purposes. Check availability with which surf. If available:

# Generate to a temp file (use --aspect-ratio for control)
surf gemini "descriptive prompt" --generate-image /tmp/ve-img.png --aspect-ratio 16:9

# Base64 encode for self-containment (macOS)
IMG=$(base64 -i /tmp/ve-img.png)
# Linux: IMG=$(base64 -w 0 /tmp/ve-img.png)

# Embed in HTML and clean up
# <img src="data:image/png;base64,${IMG}" alt="descriptive alt text">
rm /tmp/ve-img.png

See ./references/css-patterns.md for image container styles (hero banners, inline illustrations, captions).

When to use: Hero banners that establish the page's visual tone. Conceptual illustrations for abstract systems that Mermaid can't express (physical infrastructure, user journeys, mental models). Educational diagrams that benefit from artistic or photorealistic rendering. Decorative accents that reinforce the aesthetic.

When to skip: Anything Mermaid or CSS handles well. Generic decoration that doesn't convey meaning. Data-heavy pages where images would distract. Always degrade gracefully — if surf isn't available, skip images without erroring. The page should stand on its own with CSS and typography alone.

Prompt craft: Match the image to the page's palette and aesthetic direction. Specify the style (3D render, technical illustration, watercolor, isometric, flat vector, etc.) and mention dominant colors from your CSS variables. Use --aspect-ratio 16:9 for hero banners, --aspect-ratio 1:1 for inline illustrations. Keep prompts specific — "isometric illustration of a message queue with cyan nodes on dark navy background" beats "a diagram of a queue."

3. Style

Apply these principles to every diagram:

Typography is the diagram. Pick a distinctive font pairing from the list in ./references/libraries.md. Every page should use a different pairing from recent generations.

Forbidden as --font-body: Inter, Roboto, Arial, Helvetica, system-ui alone. These are AI slop signals.

Good pairings (use these):

• DM Sans + Fira Code (technical, precise)
• Instrument Serif + JetBrains Mono (editorial, refined)
• IBM Plex Sans + IBM Plex Mono (reliable, readable)
• Bricolage Grotesque + Fragment Mono (bold, characterful)
• Plus Jakarta Sans + Azeret Mono (rounded, approachable)

Load via <link> in <head>. Include a system font fallback in the font-family stack for offline resilience.

Color tells a story. Use CSS custom properties for the full palette. Define at minimum: --bg, --surface, --border, --text, --text-dim, and 3-5 accent colors. Each accent should have a full and a dim variant (for backgrounds). Name variables semantically when possible (--pipeline-step not --blue-3). Support both themes.

Forbidden accent colors: #8b5cf6 #7c3aed #a78bfa (indigo/violet), #d946ef (fuchsia), the cyan-magenta-pink combination. These are Tailwind defaults that signal zero design intent.

Good accent palettes (use these):

• Terracotta + sage (#c2410c, #65a30d) — warm, earthy
• Teal + slate (#0891b2, #0369a1) — technical, precise
• Rose + cranberry (#be123c, #881337) — editorial, refined
• Amber + emerald (#d97706, #059669) — data-focused
• Deep blue + gold (#1e3a5f, #d4a73a) — premium, sophisticated

Put your primary aesthetic in :root and the alternate in the media query:

/* Light-first (editorial, paper/ink, blueprint): */
:root { /* light values */ }
@media (prefers-color-scheme: dark) { :root { /* dark values */ } }

/* Dark-first (neon, IDE-inspired, terminal): */
:root { /* dark values */ }
@media (prefers-color-scheme: light) { :root { /* light values */ } }

Surfaces whisper, they don't shout. Build depth through subtle lightness shifts (2-4% between levels), not dramatic color changes. Borders should be low-opacity rgba (rgba(255,255,255,0.08) in dark mode, rgba(0,0,0,0.08) in light) — visible when you look, invisible when you don't.

Backgrounds create atmosphere. Don't use flat solid colors for the page background. Subtle gradients, faint grid patterns via CSS, or gentle radial glows behind focal areas. The background should feel like a space, not a void.

Visual weight signals importance. Not every section deserves equal visual treatment. Executive summaries and key metrics should dominate the viewport on load (larger type, more padding, subtle accent-tinted background zone). Reference sections (file maps, dependency lists, decision logs) should be compact and stay out of the way. Use <details>/<summary> for sections that are useful but not primary — the collapsible pattern is in ./references/css-patterns.md.

Surface depth creates hierarchy. Vary card depth to signal what matters. Hero sections get elevated shadows and accent-tinted backgrounds (ve-card--hero pattern). Body content stays flat (default .ve-card). Code blocks and secondary content feel recessed (ve-card--recessed). See the depth tiers in ./references/css-patterns.md. Don't make everything elevated — when everything pops, nothing does.

Animation earns its place. Staggered fade-ins on page load are almost always worth it — they guide the eye through the diagram's hierarchy. Mix animation types by role: fadeUp for cards, fadeScale for KPIs and badges, drawIn for SVG connectors, countUp for hero numbers. Hover transitions on interactive-feeling elements make the diagram feel alive. Always respect prefers-reduced-motion. CSS transitions and keyframes handle most cases. For orchestrated multi-element sequences, anime.js via CDN is available (see ./references/libraries.md).

Forbidden animations:

• Animated glowing box-shadows (@keyframes glow { box-shadow: 0 0 20px... }) — this is AI slop
• Pulsing/breathing effects on static content
• Continuous animations that run after page load (except for progress indicators)

Keep animations purposeful: entrance reveals, hover feedback, and user-initiated interactions. Nothing should glow or pulse on its own.

4. Deliver

Output location: Write to ~/.agent/diagrams/. Use a descriptive filename based on content: modem-architecture.html, pipeline-flow.html, schema-overview.html. The directory persists across sessions.

Open in browser:

• macOS: open ~/.agent/diagrams/filename.html
• Linux: xdg-open ~/.agent/diagrams/filename.html

Tell the user the file path so they can re-open or share it.

Diagram Types

Architecture / System Diagrams

Two approaches depending on what matters more:

Text-heavy overviews (card content matters more than connections): CSS Grid with explicit row/column placement. Sections as rounded cards with colored borders and monospace labels. Vertical flow arrows between sections. Nested grids for subsystems. The reference template at ./templates/architecture.html demonstrates this pattern. Use when cards need descriptions, code references, tool lists, or other rich content that Mermaid nodes can't hold.

Topology-focused diagrams (connections matter more than card content): Use Mermaid. A graph TD or graph LR with custom themeVariables produces proper diagrams with automatic edge routing. Use when the point is showing how components connect rather than describing what each component does in detail.

Flowcharts / Pipelines

Use Mermaid. Automatic node positioning and edge routing produces proper diagrams with connecting lines, decision diamonds, and parallel branches — dramatically better than CSS flexbox with arrow characters. Use graph TD for top-down or graph LR for left-right. Color-code node types with Mermaid's classDef or rely on themeVariables for automatic styling.

Sequence Diagrams

Use Mermaid. Lifelines, messages, activation boxes, notes, and loops all need automatic layout. Use Mermaid's sequenceDiagram syntax. Style actors and messages via CSS overrides on .actor, .messageText, .activation classes.

Data Flow Diagrams

Use Mermaid. Data flow diagrams emphasize connections over boxes — exactly what Mermaid excels at. Use graph LR or graph TD with edge labels for data descriptions. Thicker, colored edges for primary flows. Source/sink nodes styled differently from transform nodes via Mermaid's classDef.

Schema / ER Diagrams

Use Mermaid. Relationship lines between entities need automatic routing. Use Mermaid's erDiagram syntax with entity attributes. Style via themeVariables and CSS overrides on .er.entityBox and .er.relationshipLine.

State Machines / Decision Trees

Use Mermaid. Use stateDiagram-v2 for states with labeled transitions. Supports nested states, forks, joins, and notes. Decision trees can use graph TD with diamond decision nodes.

stateDiagram-v2 label caveat: Transition labels have a strict parser — colons, parentheses, <br/>, HTML entities, and most special characters cause silent parse failures ("Syntax error in text"). If your labels need any of these (e.g., cancel(), curate: true, multi-line labels), use flowchart LR instead with rounded nodes and quoted edge labels (|"label text"|). Flowcharts handle all special characters and support <br/> for line breaks. Reserve stateDiagram-v2 for simple single-word or plain-text labels.

Mind Maps / Hierarchical Breakdowns

Use Mermaid. Use mindmap syntax for hierarchical branching from a root node. Mermaid handles the radial layout automatically. Style with themeVariables to control node colors at each depth level.

Data Tables / Comparisons / Audits

Use a real <table> element — not CSS Grid pretending to be a table. Tables get accessibility, copy-paste behavior, and column alignment for free. The reference template at ./templates/data-table.html demonstrates all patterns below.

Use proactively. Any time you'd render an ASCII box-drawing table in the terminal, generate an HTML table instead. This includes: requirement audits (request vs plan), feature comparisons, status reports, configuration matrices, test result summaries, dependency lists, permission tables, API endpoint inventories — any structured rows and columns.

Layout patterns:

• Sticky <thead> so headers stay visible when scrolling long tables
• Alternating row backgrounds via tr:nth-child(even) (subtle, 2-3% lightness shift)
• First column optionally sticky for wide tables with horizontal scroll
• Responsive wrapper with overflow-x: auto for tables wider than the viewport
• Column width hints via <colgroup> or th widths — let text-heavy columns breathe
• Row hover highlight for scanability

Status indicators (use styled <span> elements, never emoji):

• Match/pass/yes: colored dot or checkmark with green background
• Gap/fail/no: colored dot or cross with red background
• Partial/warning: amber indicator
• Neutral/info: dim text or muted badge

Cell content:

• Wrap long text naturally — don't truncate or force single-line
• Use <code> for technical references within cells
• Secondary detail text in <small> with dimmed color
• Keep numeric columns right-aligned with tabular-nums

Timeline / Roadmap Views

Vertical or horizontal timeline with a central line (CSS pseudo-element). Phase markers as circles on the line. Content cards branching left/right (alternating) or all to one side. Date labels on the line. Color progression from past (muted) to future (vivid).

Dashboard / Metrics Overview

Card grid layout. Hero numbers large and prominent. Sparklines via inline SVG <polyline>. Progress bars via CSS linear-gradient on a div. For real charts (bar, line, pie), use Chart.js via CDN (see ./references/libraries.md). KPI cards with trend indicators (up/down arrows, percentage deltas).

Slide Deck Mode

An alternative output format for presenting content as a magazine-quality slide presentation instead of a scrollable page. Opt-in only — the agent generates slides when the user invokes /generate-slides, passes --slides to an existing prompt (e.g., /diff-review --slides), or explicitly asks for a slide deck. Never auto-select slide format.

Before generating slides, read ./references/slide-patterns.md (engine CSS, slide types, transitions, nav chrome, presets) and ./templates/slide-deck.html (reference template showing all 10 types). Also read ./references/css-patterns.md for shared patterns and ./references/libraries.md for Mermaid/Chart.js theming.

Slides are not pages reformatted. They're a different medium. Each slide is exactly one viewport tall (100dvh) with no scrolling. Typography is 2–3× larger. Compositions are bolder. The agent composes a narrative arc (impact → context → deep dive → resolution) rather than mechanically paginating the source.

Content completeness. Changing the medium does not mean dropping content. Follow the "Planning a Deck from a Source Document" process in slide-patterns.md before writing any HTML: inventory the source, map every item to slides, verify coverage. Every section, decision, data point, specification, and collapsible detail from the source must appear in the deck. If a plan has 7 sections, the deck covers all 7. If there are 6 decisions, present all 6 — not the 2 that fit on one slide. Collapsible details in the source become their own slides. Add more slides rather than cutting content. A 22-slide deck that covers everything beats a 13-slide deck that looks polished but is missing 40% of the source.

Slide types (10): Title, Section Divider, Content, Split, Diagram, Dashboard, Table, Code, Quote, Full-Bleed. Each has a defined layout in slide-patterns.md. Content that exceeds a slide's density limit splits across multiple slides — never scrolls within a slide.

Visual richness: Check which surf at the start. If surf-cli is available, generate 2–4 images (title slide background, full-bleed background, optional content illustrations) before writing HTML — see the Proactive Imagery section in slide-patterns.md for the workflow. Also use SVG decorative accents, per-slide background gradients, inline sparklines, and small Mermaid diagrams. Visual-first, text-second.

Compositional variety: Consecutive slides must vary spatial approach — centered, left-heavy, right-heavy, split, edge-aligned, full-bleed. Three centered slides in a row means push one off-axis.

Curated presets: Four slide-specific presets as starting points (Midnight Editorial, Warm Signal, Terminal Mono, Swiss Clean) plus the existing 8 aesthetic directions adapted for slides. Pick one and commit. See slide-patterns.md for preset CSS values.

--slides flag on existing prompts: When a user passes --slides to /diff-review, /plan-review, /project-recap, or other prompts, the agent gathers data using the prompt's normal data-gathering instructions, then presents the content as a slide deck instead of a scrollable page. The slide version tells the same story with different structure and pacing — but the same breadth of coverage. Don't use the slide format as an excuse to summarize or skip sections that the scrollable version would have included.

File Structure

Every diagram is a single self-contained .html file. No external assets except CDN links (fonts, optional libraries). Structure:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Descriptive Title</title>
  <link href="https://fonts.googleapis.com/css2?family=...&display=swap" rel="stylesheet">
  <style>
    /* CSS custom properties, theme, layout, components — all inline */
  </style>
</head>
<body>
  <!-- Semantic HTML: sections, headings, lists, tables, inline SVG -->
  <!-- No script needed for static CSS-only diagrams -->
  <!-- Optional: <script> for Mermaid, Chart.js, or anime.js when used -->
</body>
</html>

Quality Checks

Before delivering, verify:

• The squint test: Blur your eyes. Can you still perceive hierarchy? Are sections visually distinct?
• The swap test: Would replacing your fonts and colors with a generic dark theme make this indistinguishable from a template? If yes, push the aesthetic further.
• Both themes: Toggle your OS between light and dark mode. Both should look intentional, not broken.
• Information completeness: Does the diagram actually convey what the user asked for? Pretty but incomplete is a failure.
• No overflow: Resize the browser to different widths. No content should clip or escape its container. Every grid and flex child needs min-width: 0. Side-by-side panels need overflow-wrap: break-word. Never use display: flex on <li> for marker characters — it creates anonymous flex items that can't shrink, causing lines with many inline <code> badges to overflow. Use absolute positioning for markers instead. See the Overflow Protection section in ./references/css-patterns.md.
• Mermaid zoom controls: Every .mermaid-wrap container must have zoom controls (+/−/reset buttons), Ctrl/Cmd+scroll zoom, and click-and-drag panning. Complex diagrams render too small without them. The cursor should change to grab when zoomed in and grabbing while dragging. See ./references/css-patterns.md for the full pattern.
• File opens cleanly: No console errors, no broken font loads, no layout shifts.

Anti-Patterns (AI Slop)

These patterns are explicitly forbidden. They signal "AI-generated template" and undermine the skill's purpose of producing distinctive, high-quality diagrams. Review every generated page against this list.

Typography

Forbidden fonts as primary --font-body:

• Inter — the single most overused AI default
• Roboto, Arial, Helvetica — generic system fallbacks promoted to primary
• system-ui, sans-serif alone — no character, no intent

Required: Pick from the font pairings in ./references/libraries.md. Every generation should use a different pairing from the last.

Color Palette

Forbidden accent colors:

• Indigo-500/violet-500 (#8b5cf6, #7c3aed, #a78bfa) — Tailwind's default purple range
• The cyan + magenta + pink neon gradient combination (#06b6d4 → #d946ef → #f472b6)
• Any palette that could be described as "Tailwind defaults with purple/pink/cyan accents"

Forbidden color effects:

• Gradient text on headings (background: linear-gradient(...); background-clip: text;) — this screams AI-generated
• Animated glowing box-shadows on cards (box-shadow: 0 0 20px var(--glow); animation: glow 2s...)
• Multiple overlapping radial glows in accent colors creating a "neon haze"

Required: Build palettes from the reference templates (terracotta/sage, teal/cyan, rose/cranberry, slate/blue) or derive from real IDE themes (Dracula, Nord, Solarized, Gruvbox, Catppuccin). Accents should feel intentional, not default.

Section Headers

Forbidden:

• Emoji icons in section headers (🏗️, ⚙️, 📁, 💻, 📅, 🔗, ⚡, 🔧, 📦, 🚀, etc.)
• Section headers that all use the same icon-in-rounded-box pattern

Required: Use styled monospace labels with colored dot indicators (see .section-label in templates), numbered badges (section__num pattern), or asymmetric section dividers. If an icon is genuinely needed, use an inline SVG that matches the palette — not emoji.

Layout & Hierarchy

Forbidden:

• Perfectly centered everything with uniform padding
• All cards styled identically with the same border-radius, shadow, and spacing
• Every section getting equal visual treatment — no hero/primary vs. secondary distinction
• Symmetric layouts where left and right halves mirror each other

Required: Vary visual weight. Hero sections should dominate (larger type, more padding, accent-tinted background). Reference sections should feel compact. Use the depth tiers (hero → elevated → default → recessed). Asymmetric layouts create interest.

Template Patterns

Forbidden:

• Three-dot window chrome (red/yellow/green dots) on code blocks — this is a cliché
• KPI cards where every metric has identical gradient text treatment
• "Neon Dashboard" as an aesthetic choice — it always produces generic results
• Gradient meshes with pink/purple/cyan blobs in the background

Required: Code blocks use a simple header with filename or language label. KPI cards vary by importance — hero numbers for the primary metric, subdued treatment for supporting metrics. Pick aesthetics with natural constraints: Blueprint (must feel technical/precise), Editorial (must have generous whitespace and serif typography), Paper/ink (must feel warm and informal).

The Slop Test

Before delivering, apply this test: Would a developer looking at this page immediately think "AI generated this"? The telltale signs:

1. Inter or Roboto font with purple/violet gradient accents
2. Every heading has background-clip: text gradient
3. Emoji icons leading every section
4. Glowing cards with animated shadows
5. Cyan-magenta-pink color scheme on dark background
6. Perfectly uniform card grid with no visual hierarchy
7. Three-dot code block chrome

If two or more of these are present, the page is slop. Regenerate with a different aesthetic direction — Editorial, Blueprint, Paper/ink, or a specific IDE theme. These constrained aesthetics are harder to mess up because they have specific visual requirements that prevent defaulting to generic patterns.