name: svg-diagram description: SVG diagramming conventions blending a technical look with CJK-friendly typography. Use when creating flowcharts, architecture diagrams, and similar SVG figures. For one-shot generation, prefer invoking it from a subagent so the main context does not have to carry this skill plus the SVG XML; for multi-round tweaking, use it directly in the main context.

SVG Diagramming Conventions

Output location and referencing

Diagrams go in SVG, never ASCII art. That rule decides whether to draw; this skill covers how, starting with where the file lands.

• Put the file in an assets/ directory next to the document (e.g. docs/foo.md → docs/assets/foo-arch.svg)
• Reference it from markdown with a relative path, ![title](assets/xxx.svg). Do not inline SVG XML.
• When data in the document changes, the corresponding SVG must be updated too. A figure that contradicts the prose beside it is worse than no figure

Core principles

Get it right on the first pass

The first SVG you generate must already satisfy every item in the verification checklist at the end of this document. Do not rely on user feedback to fix basic layout problems (spacing, padding, alignment, viewBox clipping). After generating, walk the checklist yourself and fix anything you find before showing the result.

No overlapping elements

• Text must not sit on top of boxes or lines
• Lines must not cut through boxes (unless the line is an arrow terminating at that box)
• Keep 10–20px between text and lines
• For spacing between sibling/adjacent boxes see the "Block spacing" section below (single standard: ≥25px, 25–30px recommended)
• Put color-key legends outside the diagram body (bottom or side), never overlapping the content area

<!-- ✅ Correct: label sits beside the line -->
<path d="M35,200 C 35,120 ..." .../>
<text x="55" y="200">Label text</text>  <!-- 20px clearance -->

<!-- ❌ Wrong: label sits on the line -->
<text x="35" y="200">Label text</text>

Visual balance

The left and right halves should carry similar visual weight; add or remove annotation boxes to even them out.

Layout rules

Centering

content width = right edge of rightmost element - left edge of leftmost element
left margin   = (viewBox width - content width) / 2

Center the title on the content center, not the viewBox center (they differ whenever the content is asymmetric):

<!-- content center = (content left edge + content right edge) / 2 -->
<text x="[content center x]" y="[top_padding + font_ascent]" text-anchor="middle">Title</text>

Only when the content is left-right symmetric does content center x = viewBox width / 2. When it is asymmetric, center the whole group with <g transform="translate(...)"> and update the title's x to the new content center as well.

Shifting everything after the fact

If you only notice asymmetric left/right (or top/bottom) padding after the SVG is finished, you do not need to touch every coordinate. Wrap the content in one <g transform="translate(dx, dy)">:

<svg viewBox="0 0 800 460" ...>
  <defs>...</defs>
  <g transform="translate(22, 0)">
    <!-- all content here, coordinates unchanged -->
  </g>
</svg>

Computing the offset: dx = (right padding - left padding) / 2, where padding is the distance from the viewBox edge to the nearest content element.

• dx > 0: shift content right (use when content sits too far left)
• dx < 0: shift content left (use when content sits too far right)

When to use it: the content as a whole is off-center and you do not want to edit every x coordinate. Downside: the coordinates in the file no longer equal rendered positions, so later edits require mentally subtracting the offset — if a larger layout rework is coming, fold the offset into the individual coordinates and drop the <g>.

viewBox margins

The title is part of the content, so top and bottom margins are measured from the title:

title y      = margin + font ascent (≈ font-size × 0.75)
viewBox height = bottom y of content + margin

Recommended margin: 20–25px

<!-- Example: 16px title, 20px margin -->
<!-- title y = 20 + 16×0.75 ≈ 32 -->
<!-- content bottom 270px, viewBox height = 270 + 25 = 295 -->
<svg viewBox="0 0 680 295" ...>
  <text x="340" y="32" font-size="16">Title</text>
  ...
</svg>

Box layout

• Boxes in the same row differ in size by ≤60px; text is centered (text-anchor="middle")
• Boxes in the same column share a center line
• An outer box fully encloses the inner boxes: outer size = content size + padding × 2

Dashed grouping boxes (containers)

Used to group related boxes together (e.g. "Server", "Client", "Employee instances").

Style consistency: within one diagram, every dashed grouping box must share these attributes:

• stroke-dasharray (recommended 6,4)
• rx (corner radius, recommended 8–12)
• fill (recommended #f8fafc or none)
• Inner padding (recommended 15–20px)
• Title font size (recommended 11px, to distinguish it from the 12px box body text)

Title placement: put the group title inside the top-left corner of the box (x = box x + 10, y = box y + 14) using the secondary text color #64748b.

Vertical-centering trap: compute the group box's vertical position from the combined height of title + inner content, not from the box alone. With a title, the top of the box is occupied for roughly 20–25px, and inner boxes start below it:

<!-- ✅ Group box: title + content laid out as a whole -->
<!-- box top y=100, title takes 20px, inner boxes start at y=125 -->
<rect x="50" y="100" width="200" height="120" rx="10"
      stroke="#94a3b8" stroke-dasharray="6,4" fill="#f8fafc"/>
<text x="60" y="114" font-size="11" fill="#64748b">Server</text>
<!-- inner boxes -->
<rect x="65" y="125" width="170" height="36" rx="6" .../>
<rect x="65" y="170" width="170" height="36" rx="6" .../>

Connectors pointing at a group: when a connector logically targets a set of elements rather than one of them, terminate it on the group box boundary instead of on a single member. Alternatively, wrap the elements in a grouping box and point the arrow at that box.

Box dimensions

Derive box height from the font size so there is enough inner padding:

Where the formula comes from: font-size × 3 = top padding (≈font-size) + glyph height (≈font-size) + bottom padding (≈font-size). Scale the same ratio for non-standard font sizes.

Recommended line height: font-size × 1.5 (e.g. 18px for a 12px font)

Vertically centering text in a box (baseline positioning)

In SVG, <text y=...> is the baseline, not the top of the glyph. To center text optically inside a box:

text y = box center y + font-size × 0.35
       = box y + box height/2 + font-size × 0.35

The 0.35 factor is an empirical value for "optical glyph center to baseline" (roughly one third of the font size).

Keep the two factors apart:

• font-size × 0.75 (ascent): for elements positioned from the top, such as titles (y = top_padding + ascent)
• font-size × 0.35 (baseline offset): for vertical centering inside a box

<!-- One line: height = 12 × 3 = 36px -->
<rect x="30" y="50" width="110" height="36" rx="6" .../>
<!-- y = 50 + 36/2 + 12×0.35 = 50 + 18 + 4.2 ≈ 72 -->
<text x="85" y="72" ...>Single line</text>

<!-- Two lines: height = 36 + 18 = 54px -->
<rect x="30" y="50" width="110" height="54" rx="6" .../>
<text x="85" y="70" ...>First line</text>
<text x="85" y="88" ...>Second line</text>  <!-- 18px apart -->

Display size

<svg viewBox="0 0 750 400" width="750" xmlns="http://www.w3.org/2000/svg">

Connector rules

Choosing a connector

Use a straight L line for co-axial connections; use smooth C/Q curves whenever the path turns or routes around something. Never use right-angle elbows.

<!-- ✅ Horizontally co-axial: straight line -->
<path d="M190,77 L 320,77" .../>

<!-- ✅ Vertically co-axial: straight line -->
<path d="M130,145 L 130,213" .../>

<!-- ❌ Right-angle elbow for a turn -->
<path d="M100,100 L100,200 L200,200" .../>

<!-- ✅ Smooth curve for a turn -->
<path d="M100,100 C 100,150 150,200 200,200" .../>

Arrow rules

• Direction comes from the final path segment: rightward means x increases, downward means y increases
• Symmetric clearance: 5px between the arrow and the source box, and the same visual clearance at the target box
• Centered labels: x = (source right edge + target left edge) / 2, together with text-anchor="middle"

Fixing arrow direction on curved paths: orient="auto" aligns the arrowhead with the tangent at the end of the path. The end tangent of a C/Q curve can be skewed, which makes the arrowhead look crooked. The fix: place the second control point (cp2) so that the direction cp2 → end point is exactly the direction you want the arrowhead to face.

<!-- ❌ cp2 placed arbitrarily, arrow direction uncontrolled -->
<path d="M100,100 C 100,200 250,200 300,250" marker-end="url(#arrow)"/>

<!-- ✅ cp2 shares x with the end point, tangent naturally points down -->
<path d="M100,100 C 100,200 300,220 300,250" marker-end="url(#arrow)"/>

<!-- ✅ cp2 shares y with the end point, tangent naturally points right -->
<path d="M100,100 C 100,200 270,250 300,250" marker-end="url(#arrow)"/>

Rules for controlling arrow direction:

Computing path endpoints (5px clearance, arrowhead extends 6px past the end of the line):

Core rule: start 5px away from the source box, end 11px away from the target box (5px clearance + 6px arrowhead extension).

Because we use refX="2" (the notch at the tail of the arrowhead), the tip extends 6px (8-2=6) beyond the end of the line, and the line joins the arrowhead at the center of its notch, so the join reads as continuous.

Formulas for the four directions:

<!-- Rightward arrow →: source right edge 180, target left edge 220 -->
<!-- start: 180+5=185, end: 220-11=209, tip reaches 209+6=215 -->
<path d="M185,70 L 209,70" marker-end="url(#arrow)"/>

<!-- Leftward arrow ←: source left edge 220, target right edge 180 -->
<!-- start: 220-5=215, end: 180+11=191, tip reaches 191-6=185 -->
<path d="M215,70 L 191,70" marker-end="url(#arrow)"/>

<!-- Downward arrow ↓: source bottom 140, target top 170 -->
<!-- start: 140+5=145, end: 170-11=159, tip reaches 159+6=165 -->
<path d="M130,145 L 130,159" marker-end="url(#arrow)"/>

<!-- Upward arrow ↑: source top 170, target bottom 140 -->
<!-- start: 170-5=165, end: 140+11=151, tip reaches 151-6=145 -->
<path d="M130,165 L 130,151" marker-end="url(#arrow)"/>

Bidirectional example (two boxes with arrows going both up and down):

<!-- box A bottom=375, box B top=420 -->
<!-- downward arrow: A→B -->
<path d="M320,380 L 320,409" marker-end="url(#arrow)"/>  <!-- 375+5, 420-11 -->
<!-- upward arrow: B→A -->
<path d="M480,415 L 480,386" marker-end="url(#arrow)"/>  <!-- 420-5, 375+11 -->

Routing around obstacles

Keep detour paths at least 20px outside the obstacle's boundary:

<!-- Gateway right edge=620, detour path runs at x=650 -->
<path d="M600,313 Q 650,313 650,400 Q 650,640 635,685"
      fill="none" stroke="#a855f7" stroke-dasharray="6,4" marker-end="url(#arrow)"/>

Block spacing (single global standard)

Spacing between adjacent boxes/blocks is ≥25px, 25–30px recommended.

Breakdown: 5px start clearance + 11px end clearance and arrowhead extension + ≥6px of visible line + safety margin ≈ 25px. At least 6px of visible line, otherwise the arrow degenerates into a dot.

Stay compact: do not exceed 30px. Spacing that is too wide (>40px) makes the whole diagram feel loose and the connectors overly long. Aim for 5px / 11px at the two ends and 6–12px of visible line in between.

Overall density: when you are done, step back and judge the density — if the content area is clearly small relative to the viewBox (large blank regions), tighten spacing or shrink the viewBox. Common causes: box spacing >30px, viewBox margin >25px, excessive padding inside grouping boxes.

This is the only block-spacing standard in this document; both "No overlapping elements" and the verification checklist refer back to it.

SVG paint order (z-order)

SVG has no z-index — elements painted later sit on top. Order them like this:

<!-- 1. Bottom layer: background boxes (dashed grouping boxes, swimlanes) -->
<rect ... stroke-dasharray="6,4" fill="#f8fafc"/>

<!-- 2. Middle layer: connectors and arrows -->
<path d="..." marker-end="url(#arrow)"/>

<!-- 3. Top layer: boxes and text -->
<rect ... fill="#dbeafe"/>
<text ...>Label</text>

Common mistake: painting connectors first and the dashed background box afterwards → the connectors get covered.

Exception: cross-layer loop-back lines: connectors that must span several boxes — iteration loops, cross-region dashed lines — have to be painted after the boxes (layer 4), otherwise the boxes hide them:

<!-- 1. background boxes -->
<!-- 2. ordinary connectors -->
<!-- 3. boxes and text -->
<!-- 4. cross-layer loop-back lines (topmost, painted over the boxes) -->
<path d="..." stroke-dasharray="6,4" marker-end="url(#arrow-purple)"/>

Estimating text width (overflow protection)

Before placing text, estimate its right edge and confirm it does not intrude on neighboring elements:

Estimation formulas:

• text-anchor="start": right edge ≈ x + char count × char width
• text-anchor="middle": left/right edge ≈ x ± (char count × char width) / 2
• text-anchor="end": left edge ≈ x - char count × char width

Check before placing: text right edge + 10px < left edge of the neighbor to its right.

<!-- ❌ Text "4K tokens (= mini-batch)" starts at x=274 -->
<!-- 24 chars × 5px ≈ 120px, right edge ≈ 394, intrudes on the box at x=350 -->
<text x="274" y="115" font-size="9">4K tokens (= mini-batch)</text>

<!-- ✅ Moved below the box and centered, intrudes on nothing -->
<text x="154" y="138" font-size="9" text-anchor="middle">4K tokens (= mini-batch)</text>

Placing labels on curves

A label describing an arc or curve must not sit on the path itself (the line would run through the text) — put it on the convex or concave side of the curve:

<!-- ❌ Label at y=218 while the curve passes near y=225: the line cuts the text -->
<text x="350" y="218">Skip Connection</text>
<path d="M82,165 C 82,225 620,225 646,225" .../>

<!-- ✅ Label at y=222, lowest point of the curve at y=260, 38px apart -->
<text x="350" y="222">Skip Connection</text>
<path d="M82,149 C 82,260 600,255 640,255" .../>

Rule: keep ≥15px between the label and the nearest point on the curve. For a downward-bending curve put the label above it; for an upward-bending curve put it below.

Coordinate management

Record boundaries in comments

<!-- Gateway: x=280, y=55, width=340, height=435, right edge=620, bottom edge=490 -->
<rect x="280" y="55" width="340" height="435" .../>

When you move an element, update in lockstep

1. viewBox dimensions
2. Every arrow to/from that element (start point, end point, control points)
3. Positions of related labels
4. The dashed background/grouping box that wraps the element (swimlane, container) — the most commonly missed one
5. Other boxes aligned with it in the same row/column
6. Any other affected elements

Style rules

Fonts (required)

Every SVG must declare a CJK-capable font stack in <style> — this is non-negotiable:

<style>
  text { font-family: 'PingFang SC', 'Microsoft YaHei', 'Noto Sans CJK SC', system-ui, sans-serif; }
</style>

Fallback order: macOS (PingFang SC) → Windows (Microsoft YaHei) → Linux (Noto Sans CJK SC) → system default. Noto Sans CJK SC must be kept, otherwise server-side rendering on Linux falls back to a font with no CJK coverage.

Vertical text: <text writing-mode="tb">vertical text</text>

Colors

Base colors: primary text #1e293b, secondary text #64748b, muted text / arrows #94a3b8

Semantic colors:

Arrowhead definitions

Use a notched arrowhead rather than a plain triangle — it reads better:

<defs>
  <!-- Default gray arrow (markerUnits="userSpaceOnUse" is mandatory) -->
  <marker id="arrow" markerWidth="8" markerHeight="8" refX="2" refY="4" orient="auto" markerUnits="userSpaceOnUse">
    <path d="M0,0 L8,4 L0,8 L2,4 z" fill="#64748b"/>
  </marker>
  <!-- Semantic-color arrows (matching the box stroke colors) -->
  <marker id="arrow-blue" markerWidth="8" markerHeight="8" refX="2" refY="4" orient="auto" markerUnits="userSpaceOnUse">
    <path d="M0,0 L8,4 L0,8 L2,4 z" fill="#3b82f6"/>
  </marker>
  <marker id="arrow-orange" markerWidth="8" markerHeight="8" refX="2" refY="4" orient="auto" markerUnits="userSpaceOnUse">
    <path d="M0,0 L8,4 L0,8 L2,4 z" fill="#f59e0b"/>
  </marker>
  <marker id="arrow-green" markerWidth="8" markerHeight="8" refX="2" refY="4" orient="auto" markerUnits="userSpaceOnUse">
    <path d="M0,0 L8,4 L0,8 L2,4 z" fill="#22c55e"/>
  </marker>
  <marker id="arrow-purple" markerWidth="8" markerHeight="8" refX="2" refY="4" orient="auto" markerUnits="userSpaceOnUse">
    <path d="M0,0 L8,4 L0,8 L2,4 z" fill="#a855f7"/>
  </marker>
  <marker id="arrow-red" markerWidth="8" markerHeight="8" refX="2" refY="4" orient="auto" markerUnits="userSpaceOnUse">
    <path d="M0,0 L8,4 L0,8 L2,4 z" fill="#ef4444"/>
  </marker>
</defs>

Arrow color reference:

Key parameters:

• orient="auto" rotates the arrowhead to follow the path direction
• markerUnits="userSpaceOnUse" must be declared explicitly, otherwise the default strokeWidth scales the arrowhead with line thickness (at stroke-width=2 the arrow doubles in size and blows past the intended clearance)
• refX="2" aligns the end of the line with the center of the arrowhead's tail notch, so the join looks natural
• refY="4" centers it vertically (arrow height 8, midpoint 4)
• The arrow path M0,0 L8,4 L0,8 L2,4 z forms the notched shape, with the tip at x=8
• The tip extends 6px (8-2=6) beyond the end of the line, so the end point is computed as target edge - 11

Arrows on thick lines: when stroke-width > 1.5 (e.g. heavy dashed lines), an 8×8 arrowhead looks too small. Define a proportionally larger marker:

<!-- Large arrow for thick lines (1.5×): tip extends 12-3=9px -->
<marker id="arrow-red-lg" markerWidth="12" markerHeight="12" refX="3" refY="6"
        orient="auto" markerUnits="userSpaceOnUse">
  <path d="M0,0 L12,6 L0,12 L3,6 z" fill="#ef4444"/>
</marker>

XML special characters (high risk, always check)

SVG is XML, so special characters in text must be escaped or the entire SVG fails to render:

<!-- ❌ Wrong: unescaped & -->
<text>Load & Save</text>

<!-- ✅ Correct: escaped -->
<text>Load &amp; Save</text>

Escaping when generating SVG programmatically

When generating SVG from Python/JS, text coming from external sources (CSV, database, API) must be escaped before it is concatenated into the SVG:

def svg_escape(text):
    return str(text).replace('&','&amp;').replace('<','&lt;').replace('>','&gt;').replace('"','&quot;')

# ❌ Splicing external data directly ("Research&Development" → XML parse failure, image won't render)
svg += f'<text>{team_name}</text>'

# ✅ Escape first
svg += f'<text>{svg_escape(team_name)}</text>'

High-risk data sources: team names (contain &), requirement descriptions (contain <>), user input, file names

Troubleshooting

Verification checklist

• No overlapping elements (text, boxes, lines)
• No text right edge intrudes on a neighbor (estimated from character widths)
• ≥15px between a curve label and the nearest point on the curve
• Symmetric arrow clearance at both ends (5px), visible line segment ≥6px
• Markers declare markerUnits="userSpaceOnUse"
• Thick lines (stroke-width > 1.5) use the enlarged marker
• Connectors use C/Q curves, no right angles
• Labels centered (text-anchor="middle")
• Detour paths stay outside obstacles
• Block spacing ≥25px (25–30px recommended, see "Block spacing")
• Title centered, boxes in a row similar in size
• width attribute present, viewBox matches the content
• Box heights sufficient (one line ≥ font-size × 3)
• Top and bottom viewBox margins comparable (20–25px, measured from the top of the title)
• Left and right viewBox padding symmetric (use <g transform="translate(dx,0)"> to shift if not)
• Special characters escaped (& → &, < → <)
• Every element inside the visible viewBox (bottom = bottom edge of the lowest element + 25px)
• Every connector has a clear meaning (labeled, or its source and target are inferable from context)
• Dashed grouping boxes styled consistently (dasharray, corner radius, fill, padding, title font size)
• No large blank regions (spacing within 30px, viewBox hugs the content)

Editing workflow

1. Collect: gather the full set before touching anything

When you receive a request to modify an SVG, do not start editing immediately. First judge:

• The user gave one change → reply "anything else you want adjusted?" to get the full list in one go
• The user gave several changes → move to execution and apply them all at once

Goal: fewer round trips, so you are not re-emitting the whole SVG for every single tweak.

2. Execute: apply everything at once, with a change list

Once all edits are done, print the change list first, then show the final SVG:

Change list:
1. Title spacing 20px → 30px
2. Box A fill #dbeafe → #f3e8ff
3. Connector L1 path adjusted (routes around the new box)

Do not show the diagram after each individual edit — the user only needs the final result.

3. Layout tweaks: understand the intent and adjust dependents

When the user says "move box A 20px to the right", do not mechanically change box A's x alone. Handle the dependents too:

• Every arrow path to/from box A
• Alignment with the other boxes in box A's row
• The position of box A's text labels
• The size of the outer/background box wrapping box A

Spacing/alignment requests ("make it tighter", "left-align it", "center it") → read the overall intent and adjust all related elements in one pass, so the user does not have to iterate pixel by pixel.

svg-diagram

A house style for hand-written SVG diagrams your agent can follow — the layout arithmetic, the colour system, and a zero-dependency linter that proves it did.

Install

Paste this to your coding agent:

Install the svg-diagram skill from https://github.com/bybit-exchange/svg-diagram
for me by running: npx skills add bybit-exchange/svg-diagram -g

Or run it yourself:

npx skills add bybit-exchange/svg-diagram -g

The CLI detects which agents you have installed and writes each one's path. Drop -g to install into the current project instead.

Every path is named from the skill's frontmatter name, not from where the skill sits here, so moving files in this repository doesn't change them.

SKILL.md is at the repository root, so the install copies the root and svg-lint comes along with the skill text. The linter has no dependencies, so it runs from wherever it landed:

node ~/.claude/skills/svg-diagram/tools/svg-lint/bin/svg-lint.mjs diagram.svg

If you only want the skill text, take the one file the agent reads:

mkdir -p ~/.claude/skills/svg-diagram
curl -fsSL https://raw.githubusercontent.com/bybit-exchange/svg-diagram/main/SKILL.md \
  -o ~/.claude/skills/svg-diagram/SKILL.md

The skill works on its own that way; svg-lint is what you give up.

Then start a new session and ask for a diagram — the agent should announce that it's using svg-diagram.

Gallery

Ten diagrams, all drawn under this skill and all lint clean. Each one is here for the rule it demonstrates.

How an agent loads a skill

Two dashed containers side by side. Connectors cross the channel between them, and a colour change marks the point where a request matches.

The authoring loop

A cross-layer loop-back line, painted after the boxes so they don't cover it.

Where the lint gate sits

A self-call that leaves its lifeline and curves back to it, its second control point sharing the end point's y so the arrowhead closes level and points at the participant rather than down the lifeline.

From a data API to a document figure

CJK labels sized from the CJK column of the width table — one full font size per character, 12px rather than 7.

The life of a skill in this repo

One semantic colour triple per state. Each forward arrow carries the colour of the state it leaves.

What's in this repository

A dashed border only where the contents are actually drawn — gallery/ and assets/ are directories too, but their members aren't in the figure, so they stay plain boxes.

One command, every agent

A one-to-many fan-out whose branch curves keep each second control point level with the end point, so every arrowhead lands pointing right.

Why the font stack cannot be dropped

A contrast pair built from two semantic triples: the working paths in green, the branch that fails in pink.

Tiered model routing behind one gateway

A symmetric fan-out and convergence, one triple per tier. Only the middle leg leaves the rule box's bottom edge; the two outer ones leave its sides.

A/B benchmark with a model as judge

A dashed group box around exactly the steps that repeat. The return edge is painted last, so it stays legible where it crosses the wall.

What the skill pins down

Every diagram also paints its own white canvas rect as the first element, so it reads as a light card on GitHub's dark theme instead of dark text on a dark background. That isn't theme switching. The diagram carries one colour set, and the rect exists only so that set stays readable wherever the file is embedded.

The full rules — the character width tables, the six arrowhead colour variants, the coordinate bookkeeping, and a twenty-item verification checklist — are in SKILL.md, which is the single source of truth.

Why

• Checked on the real artifact. The linter reads the finished SVG, not an intermediate format. Nothing sits between the receipt and the file you ship.
• Zero dependencies. svg-lint is plain Node with no packages. It runs in a fresh clone, with no install step and no lockfile.
• Placed, not auto-laid-out. The skill hands the agent the arithmetic — box height, baseline offset, arrow clearance, block spacing — so every element lands somewhere chosen rather than somewhere a layout engine picked.
• Findings name the fix. A failure reports the value it found and the value it should hold: viewBox: 11 → 20–25, not "the margin looks wrong".
• CJK-safe by default. A mandatory font stack, plus separate character-width tables for Latin and CJK, so labels are checked for overflow before they're placed.
• Reviewable as text. Every coordinate is a literal, annotated with a comment explaining why it holds that value, so a change to a diagram reads as a diff instead of a re-render.
• Plain SVG out. No runtime, no viewer, no JavaScript. It renders in a README, a docs site, a PDF and a terminal preview.

The lint gate

svg-lint reads the finished SVG and reports what the house style forbids. It's a maintainer tool, run by hand. Nothing invokes it for you, so run it before you hand a diagram over.

node tools/svg-lint/bin/svg-lint.mjs diagram.svg
node tools/svg-lint/bin/svg-lint.mjs diagram.svg --json

Try it on a deliberately broken file:

printf '%s' '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 200 60" width="200"><text x="50" y="20" font-size="12">Load & Save</text></svg>' > /tmp/broken.svg
node tools/svg-lint/bin/svg-lint.mjs /tmp/broken.svg

That reports 3 errors and 7 warnings and exits 1: the unescaped &, the missing font stack, the missing white canvas rect, an off-palette fill, four viewBox margins outside the 20–25px range, and asymmetric margins on both axes. Each finding carries the id of the check that raised it and a repair line:

  1:1  error  No <style> rule declares font-family for text  [font-stack/missing-font-stack]
         repair: font-family: absent → 'PingFang SC', 'Microsoft YaHei', 'Noto Sans CJK SC', system-ui, sans-serif · SKILL.md marks this non-negotiable

The 12 checks cover XML escaping, viewBox clipping, the font stack, box height, baseline offset, block spacing, arrow markers, text overflow, overlap, light-background fallback, palette conformance and connector geometry. A thirteenth id, document-model, raises no findings of its own. It's how the model layer reports what it couldn't read, so the geometry checks never draw c