Svg Check

Sub-Skill: SVG Check

Purpose. Catch text-overflow and foreign-rect-intersection bugs in SVG diagrams before commit. LLM eyeball review at 4× zoom misses these bug classes consistently — measurement is the only reliable test.

The acceptance test is the script output. Not your visual judgment.

When to apply

Apply this skill whenever:

• you are editing an existing SVG (*.svg in any docs/diagrams folder),
• you are producing a new SVG from scratch,
• a designer agent reports an SVG as "clean" — verify with the script,
• you are reviewing a PR that touches *.svg.

The two bug classes the script catches

1. OVERFLOW (own-container): a <text> whose rendered bbox extends past the bounds of its containing <rect> (in the same <g>). Caught by getBBox() measurement, tolerance 2 px.

2. FOREIGN-RECT INTERSECT: a <text> whose viewport bbox intersects a <rect> that is not an ancestor of the text — i.e. a tagline ascender that touches a structural box above/below it. Caught by getBoundingClientRect() intersection, tolerance 2 px.

Both classes filter false-positives: rects smaller than 40 × 18 (legend swatches) are not treated as containers; texts that start more than 5 px outside a rect's horizontal range are not treated as contained.

How to run

The script lives next to this file: overflow-check.js. It needs Playwright installed once per machine.

One-time setup

# From the skill folder
cd skills/svg-check
bash setup.sh

Or manually:

npm install playwright
npx playwright install chromium --with-deps

Run on one SVG

node skills/svg-check/overflow-check.js path/to/diagram.svg

Run on all SVGs in a folder

for svg in path/to/*.svg; do
  out=$(node skills/svg-check/overflow-check.js "$svg" 2>&1)
  if echo "$out" | grep -q "FOUND"; then
    echo "FAIL: $svg"; echo "$out" | grep -E "FOUND|  \[|  \""
  fi
done

The script exits non-zero when issues are found — suitable for use as a pre-commit gate or CI step.

Acceptance criteria

The script output must contain both of these lines, verbatim, for every SVG in scope:

OVERFLOW: CLEAN — 0 text overflows past their containing rect
FOREIGN-RECT INTERSECT: CLEAN — 0 text-vs-foreign-rect intersections

Anything else means not done. Fix the SVG (shorten text, widen rect, move element, change font-size) and re-run until both lines are CLEAN.

In addition, after the script is CLEAN, render a Playwright screenshot in light + dark mode and visually cross-check for bug classes the script does not cover (see § Limits below).

How to fix common overflow patterns

Examples

See EXAMPLES.md for real before/after fixes with script output.

Limits — what the script does NOT catch

These remain eyeball-only for now. When a missed bug class surfaces, extend the script with a new check class — do not rely on agent self-reporting.

• Text-vs-line overlaps: a <text> crossing an <line> arrow.
• ≥12 px clearance between text-baseline and the nearest line below it.
• Sibling text overlaps: two <text> elements at the same coords.
• Color contrast ratio in dark mode.
• Glyph render quality at small sizes (≤ 10 px).

Why this skill exists (incident history)

• 2026-05-11 #1: a four-designer parallel review declared architecture.svg clean. The GEMINI CLI loader-tag overflowed its 200 px box by 42.6 px. No agent measured.
• 2026-05-11 #2: a follow-up three-cycle eyeball review missed that the tagline ascenders intruded into the folder-strip border above. The fix was a 20 px viewBox extension; the bug was a 2 px overlap that the agents could not detect by sight.

The script was built after the second miss. It catches both bug classes in under 5 seconds.

The rule that follows from these incidents: don't trust agent self-reports of "no issues at 4× zoom". Trust the measurement.

Required output for "done"

When reporting work on any SVG, paste the script output verbatim — both before the fix (showing the bug) and after the fix (showing CLEAN). Without that paste, the work is not done.