Diagram Design

Diagram Design

Create visual diagrams as self-contained HTML files with inline SVG and CSS, following an opinionated editorial design system.

Fourteen diagram types. One shared design system, complexity budget, and taste gate. Type-specific conventions live in references/ and are loaded only when you pick a type.

0. First-time setup — style guide gate

Before generating your first diagram in a new project, verify the style guide has been customized.

Open references/style-guide.md and check the default tokens. If they're still the shipped defaults (paper #faf7f2, ink #1c1917, accent #b5523a rust), pause and ask the user:

"This is your first Schematic in this project. The style guide is still at the default (neutral stone + rust). Do you want to customize it to match your brand first? Options: (a) run onboarding — I'll pull colors and fonts from your website, (b) paste your tokens manually, (c) proceed with the default for now."

Then branch:

• (a) → follow references/onboarding.md to fetch the site, extract palette + fonts, propose a diff, and write style-guide.md.
• (b) → accept the user's tokens and write them into style-guide.md under a new "Custom tokens" section.
• (c) → proceed; optionally remind the user they can run onboarding later.

Once the style guide has been customized (or the user explicitly opted for default), skip this gate on subsequent runs. A simple way to detect customization: if the accent value in style-guide.md differs from #b5523a, assume custom.

Don't silently ship default-skinned diagrams into a branded project — that's the failure mode this gate exists to prevent.

1. Philosophy

The highest-quality move is usually deletion.

From .impeccable.md: "Confident restraint. Earn every element. One color accent, two families, a small spacing vocabulary. If removing it wouldn't hurt the page, remove it."

Applied to schematics:

• Every node represents a distinct idea. Two nodes that always travel together are one node.
• Every connection carries information. If the relationship is obvious from layout, remove the line.
• Coral is editorial, not a flag. 1–2 focal nodes per diagram. Using it on 5 nodes erases the signal.
• The schematic isn't done when everything is added. It's done when nothing can be removed.

Target density: 4/10. Enough to be technically complete. Not so dense it needs a guide. Above 9 nodes, it's probably two diagrams.

2. When to Use

Use for any of the 14 diagram types (§3) when a reader will learn more from a visual than from prose, a table, or a bulleted list.

Don't use for:

• Quick unicode diagrams → use wiretext.
• Lists of things → table or bullets.
• Simple before/after → table.
• One-shape "diagrams" → just write the sentence.

Before drawing, ask: Would the reader learn more from this than from a well-written paragraph? If no, don't draw.

3. Diagram Types

Selection guide

Rules of thumb:

• If a 3-column table communicates the same thing, pick the table.
• If you're combining two types, pick the dominant axis — don't hybridize grammars.
• If you're past the complexity budget (§7), split into an overview + detail.

Always load the relevant references/type-*.md before drawing — it contains layout conventions, anti-patterns, and example files for that type.

4. Universal Anti-patterns

These mark "AI slop" schematics of any type:

Type-specific anti-patterns live in each references/type-*.md.

5. Design System

The design system is skinnable. All colors, typography, and tokens live in a single source of truth — references/style-guide.md. This file describes semantic roles (paper, ink, muted, accent, link, …). The default skin is a cool editorial palette (white-smoke paper, jet-black ink, atomic-tangerine accent, blue-slate muted, silver hairlines); to apply your own brand, either edit style-guide.md directly or run the URL-based flow described in references/onboarding.md.

When specs below or in type references mention "ink", "accent", "muted", etc., look up the current hex value in style-guide.md.

Semantic roles (at a glance)

Focal rule: accent goes on 1–2 elements max. Everything else is ink / muted / soft. If you're tempted to accent 4 things, you haven't decided what's focal yet.

Node type → treatment

Typography (summary — full spec in style-guide.md)

• Title — Instrument Serif, 1.75rem, 400 — H1 only
• Node name — Geist (sans), 12px, 600 — human-readable labels
• Sublabel — Geist Mono, 9px — ports, URLs, field types
• Eyebrow / tag — Geist Mono, 7–8px, uppercase, tracked — type tags, axis labels
• Arrow label — Geist Mono, 8px — annotation on arrows
• Editorial aside — Instrument Serif italic, 14px — callouts only

Mono is for technical content. Names are Geist sans. Page title is Instrument Serif. Italic Instrument Serif is reserved for annotation callouts. Never JetBrains Mono as a blanket "dev" font.

<link href="https://fonts.googleapis.com/css2?family=Instrument+Serif:ital@0;1&family=Geist:wght@400;500;600&family=Geist+Mono:wght@400;500;600&display=swap" rel="stylesheet">

6. Core SVG Primitives

Universal building blocks. Type-specialized primitives (lifeline, activation bar, region) live in the relevant references/type-*.md. Optional primitives:

• Editorial callouts → primitive-annotation.md
• Hand-drawn variant → primitive-sketchy.md

Background

Default: clean paper, no dot pattern. Single <rect> filled with paper. Don't wrap the diagram in a secondary container background — the diagram sits directly on the page.

<rect width="100%" height="100%" fill="#f5f5f5"/>

Optional: dotted paper variant. When a long-form editorial diagram benefits from textured ground (essays, hero diagrams on a dedicated page), opt in by adding the dots pattern and a second rect:

<defs>
  <pattern id="dots" width="22" height="22" patternUnits="userSpaceOnUse">
    <circle cx="1" cy="1" r="0.9" fill="rgba(45,49,66,0.10)"/>
  </pattern>
</defs>
<rect width="100%" height="100%" fill="#f5f5f5"/>
<rect width="100%" height="100%" fill="url(#dots)" opacity="0.6"/>

Don't use the dot pattern when the diagram sits inside a product page, slide, or card — the texture compounds with surrounding chrome and reads as noise.

Arrow markers (define all three, always)

<marker id="arrow" markerWidth="8" markerHeight="6" refX="7" refY="3" orient="auto">
  <polygon points="0 0, 8 3, 0 6" fill="#4f5d75"/>
</marker>
<marker id="arrow-accent" markerWidth="8" markerHeight="6" refX="7" refY="3" orient="auto">
  <polygon points="0 0, 8 3, 0 6" fill="#eb6c36"/>
</marker>
<marker id="arrow-link" markerWidth="8" markerHeight="6" refX="7" refY="3" orient="auto">
  <polygon points="0 0, 8 3, 0 6" fill="#2e5aa8"/>
</marker>

Draw arrows before boxes so z-order puts lines behind nodes.

Node box — full pattern

<!-- 1. Opaque paper mask — prevents arrows bleeding through transparent fills -->
<rect x="X" y="Y" width="W" height="H" rx="6" fill="#f5f5f5"/>
<!-- 2. Styled box -->
<rect x="X" y="Y" width="W" height="H" rx="6" fill="FILL" stroke="STROKE" stroke-width="1"/>
<!-- 3. Rectangular type tag (rx=2, NOT a pill) -->
<rect x="X+8" y="Y+6" width="28" height="12" rx="2" fill="transparent" stroke="STROKE@0.40" stroke-width="0.8"/>
<text x="X+22" y="Y+15" fill="STROKE@0.8" font-size="7" font-family="'Geist Mono', monospace"
      text-anchor="middle" letter-spacing="0.08em">API</text>
<!-- 4. Node name (Geist sans — human-readable) -->
<text x="CX" y="CY+2" fill="#2d3142" font-size="12" font-weight="600"
      font-family="'Geist', sans-serif" text-anchor="middle">Node Name</text>
<!-- 5. Technical sublabel (Geist Mono) -->
<text x="CX" y="CY+18" fill="#4f5d75" font-size="9"
      font-family="'Geist Mono', monospace" text-anchor="middle">tech:port</text>

Arrow labels — always mask

Every arrow label needs an opaque rect behind it. Without one it bleeds through the line.

<rect x="MID_X-18" y="ARROW_Y-12" width="36" height="12" rx="2" fill="#f5f5f5"/>
<text x="MID_X" y="ARROW_Y-3" fill="#7a8399" font-size="8"
      font-family="'Geist Mono', monospace" text-anchor="middle" letter-spacing="0.06em">WRITE</text>

Rules: ≤14 characters, all-caps, centered on segment midpoint, 8–10px above line. Never writing-mode vertical.

Legend — horizontal strip at the bottom

Never put the legend inside the diagram area. Place as a horizontal strip after all nodes, with a hairline separator:

<line x1="30" y1="LEGEND_Y-8" x2="VIEWBOX_W-30" y2="LEGEND_Y-8"
      stroke="rgba(45,49,66,0.10)" stroke-width="0.8"/>
<text x="30" y="LEGEND_Y+8" fill="#4f5d75" font-size="8" font-family="'Geist Mono', monospace"
      letter-spacing="0.14em">LEGEND</text>
<!-- Items — horizontal row, ~160px apart -->

Expand SVG viewBox height by ~60px.

7. Layout & Spacing

4px grid

All values — font sizes, padding, node dimensions, gaps, x/y coords — divisible by 4. Non-negotiable.

Exempt: stroke widths (0.8, 1, 1.2), opacity values, and the 22×22 dot-pattern.

Quick check: if a coordinate ends in 1, 2, 3, 5, 6, 7, 9 — fix it.

Complexity budget (per diagram)

If you exceed, split into two diagrams (overview + detail).

Page layout

1. Header — eyebrow (Geist Mono), title (Instrument Serif), optional subtitle (Geist muted).
2. Diagram container — default: clean, borderless, no background — the SVG sits directly on the page paper. Optional framed variant (for card-heavy layouts or hero placements): paper-2 bg + 1px rule border + 8px radius + 1.5rem padding + overflow-x: auto.
3. Summary cards — 2–3 col grid with varied widths (e.g., 1.1fr 1fr 0.9fr).
4. Footer — colophon in Geist Mono, muted, hairline top border.

8. Summary Card Pattern

Don't use 3 identical generic cards. Vary the treatment:

<div class="card">
  <p class="eyebrow">SECTION LABEL</p>
  <div class="card-header">
    <span class="card-dot coral"></span>
    <h3>Card Title</h3>
  </div>
  <ul><li>Item</li></ul>
</div>

Rules:

• background: #ffffff (not paper — slight lift without shadow)
• border: 1px solid rgba(45,49,66,0.12)
• border-radius: 6px, padding: 1.25rem
• No box-shadow
• Card dots: 7px, border-radius: 50% — ink / muted / coral / link / soft variants

9. Pre-Output Checklist (Taste Gate)

Run before producing any diagram.

Type fit:

• Right type for what I'm showing? (§3 selection guide)
• Would a table / paragraph do the same job? (If yes — don't draw.)
• Loaded the matching references/type-*.md?

Remove test:

• Can I remove any node? (Would a reader still understand?)
• Can I merge any two nodes? (Do they always travel together?)
• Can I remove any arrow? (Is the relationship obvious from layout?)
• Can I remove any label? (Does color or shape already signal it?)

Signal:

• Coral used on ≤2 elements? If more, which actually deserve focal status?
• Legend covers every type used — and nothing extra?
• Within the type's complexity budget (§7)?

Technical:

• Arrows drawn before boxes?
• Every arrow label has an opaque fill="#f5f5f5" rect behind it?
• Legend is a horizontal bottom strip, not floating?
• No vertical writing-mode text?
• viewBox expanded for the legend strip (~60px)?
• Every font size, coord, width, height, gap divisible by 4?

Typography:

• Human-readable names in Geist sans, not Geist Mono?
• Technical sublabels (ports, commands, URLs) in Geist Mono?
• Page title in Instrument Serif?
• Annotation callouts (if any) in italic Instrument Serif? (see primitive-annotation.md)
• No JetBrains Mono anywhere?

10. Templates & Variants

Every diagram ships in three variants (see assets/):

Sketchy variant (optional, applied to any of the above) — see primitive-sketchy.md. SVG turbulence filter wobbles strokes for a hand-drawn feel. Good for essays, not for technical docs.

To create a new diagram

1. Copy the variant closest to what you want (template.html for minimal, template-full.html for cards).
2. Load the matching references/type-<name>.md for layout conventions.
3. Replace the eyebrow, h1, and SVG body.
4. Run the §9 taste gate.

11. Output

Always produce a single self-contained .html file:

• Embedded CSS (no external except Google Fonts)
• Inline SVG (no external images)
• No JavaScript required

Renders correctly in any modern browser.

Source: cathrynlavery/diagram-design — distributed by TomeVault.