Cursor rule

1---
2description: "Extract a Google DESIGN.md file from an HTML prototype (claude.ai/design or any styled page) using Puppeteer, producing machine-readable tokens and AI-generated prose. Use when the user has an HTML prototype and wants a DESIGN.md to anchor their project's visual identity, or when seed-conventions has just scaffolded a new project."
3alwaysApply: false
4---
5 
6# Extract DESIGN.md from HTML
7 
8> **HARD GATE** — Do NOT write DESIGN.md without Puppeteer dual-pass extraction. Tokens from static HTML (Cheerio, regex, string scanning) are invalid — they miss cascade, custom properties, and Tailwind resolution.
9>
10> **HARD GATE** — Do NOT claim certainty where evidence is thin. Low-confidence color roles, component classifications, and prose assertions MUST be flagged with `<!-- AGENT NOTE: uncertain — validate during grill-me. Evidence: [what was observed] -->`.
11>
12> **HARD GATE** — Do NOT ship DESIGN.md without running `npx @google/design.md lint`. Unvalidated output is unverified output. If lint is unavailable (offline), flag prominently in terminal and in DESIGN.md prose.
13 
14## Quick Start
15 
16```bash
17# First run — extract from HTML prototype
18node extract-design/scripts/extract.js --source ./prototype.html
19 
20# From a published URL
21node extract-design/scripts/extract.js --source https://my-prototype.example.com
22 
23# With a custom name
24node extract-design/scripts/extract.js --source ./proto.html --name &quot;My Design System&quot;
25 
26# Update — re-extract from new HTML, diff against existing
27node extract-design/scripts/extract.js --source ./proto-v2.html
28 
29# Lint-only — validate existing DESIGN.md without re-extraction
30node extract-design/scripts/extract.js --lint-only
31```
32 
33## Flow
34 
351. **Launch Puppeteer** — dual-pass (light + dark) with retry + timeout. CI flags: `--headless=new --no-sandbox --disable-gpu --disable-dbus --use-gl=angle --use-angle=swiftshader`.
362. **Collect styles** — `page.evaluate()` collects computed styles from every element. Returns raw JSON to Node.js. Browser = sensor; Node = brain.
373. **Classify tokens** — modular pipeline: colors (Material 3 roles), typography (scale detection), spacing (tolerance GCD), rounded (clustering), components (visual signature + pseudo-state variants).
384. **Generate prose** — AI heuristics produce all 8 DESIGN.md sections. Overview and Do's/Don'ts flagged with agent notes.
395. **Write + validate** — serialize to `specs/tech-architecture/DESIGN_LATEST.md`, run `npx @google/design.md lint`, report to terminal.
406. **Handoff** — writes `handoff.next_skill: grill-me` to `specs/state.yaml` with uncertain decisions context.
41 
42## Inputs
43 
44| Parameter | Required | Description |
45|-----------|----------|-------------|
46| `--source <file\|url>` | First run: yes. Update: optional | HTML prototype path or URL |
47| `--name <string>` | No | Design system name (defaults to `<title>` or directory name) |
48| `--lint-only` | No | Validate existing DESIGN.md without re-extraction |
49 
50## Output
51 
52- `specs/tech-architecture/DESIGN_LATEST.md` — replaces `DESIGN_PLAN_LATEST.md` as the canonical design artifact
53- Terminal summary: token counts, component count, lint result, uncertain decisions
54- Structured JSON log to stderr: extraction events, timing, counts
55- `specs/state.yaml` → `handoff.next_skill: grill-me` with context
56 
57## Error Tiers
58 
59| Tier | Condition | Response |
60|------|-----------|----------|
61| Fatal | No Chrome, page load timeout after retries | Exit non-zero, suggest fixes |
62| Degraded | Zero colors, zero typography, SPA shell | Write DESIGN.md with degradation warning |
63| Warned | Lint errors, uncertain decisions | Write DESIGN.md, flag in terminal, hand off to grill-me |
64 
65## Dependencies
66 
67- **Puppeteer** (Chrome binary) — wrapped behind `BrowserExtractor` interface for testability
68- **`@google/design.md`** (soft, via `npx`) — wrapped behind `DesignValidator` interface. Warns and skips if offline.
69 
70## verify
71 
72```bash
73node extract-design/tests/test-extraction.js
74```
75 
76See [REFERENCE.md](REFERENCE.md) for extraction algorithms and heuristics.
77 
78---
79 
80# Extract Design — Reference
81 
82## Extraction Algorithms
83 
84### Color Classification
851. Collect unique computed `background-color`, `color`, `border-color` from every DOM element.
862. Count frequency and context (text vs. bg vs. border vs. button).
873. Classify using Material 3 roles: surface = largest-area bg, on-surface = most-used text, tertiary = highest-saturation on CTAs, error = reddish.
884. Surface container levels: luminance-ordered. Hard-cap at 3 unless data supports 5.
895. Low-confidence → `<!-- AGENT NOTE -->` in Colors prose.
90 
91### Typography Classification
921. Collect unique (fontFamily, fontSize, fontWeight, lineHeight, letterSpacing) tuples.
932. Cluster by fontSize (±2px) → type scale.
943. Detect heading hierarchy from HTML tag + computed size.
954. Name levels: display-lg, headline-lg/md/sm, title-lg, body-lg/md/sm, label-lg/md/sm.
965. Parse `<link>` and `@font-face`; warn if computed font differs from declared.
97 
98### Spacing Classification
991. Collect unique padding, margin, gap values. Filter: ignore values < 3 occurrences.
1002. Compute tolerance-based GCD (0.5px tolerance).
1013. Declare base unit. Detect half-step if gcd/2 values present ≥3 times.
1024. Map: unit×1 → sm, ×2 → md, ×4 → lg, ×8 → xl.
103 
104### Rounded Classification
1051. Collect unique border-radius values. Cluster (1px tolerance).
1062. Name: none (0), sm (smallest), md (median), lg (large), xl (largest), full (9999px).
107 
108### Component Detection
109- Button: w<300px, h<64px, bg+radius set, short text. cursor:pointer is bonus.
110- Card: bg+radius+padding set, larger area.
111- Input: `<input>` or `<textarea>` tag.
112- Pseudo-state variants: force :hover, :active, :focus for high-confidence components.
113 
114### Prose Generation
115Generates all 8 DESIGN.md sections. Overview and Do's/Don'ts flagged with `<!-- AGENT NOTE: Generated from visual analysis. Grill-me should validate. -->`.
116 
117## Material 3 Token Conventions
118Colors: primary, on-primary, secondary, tertiary, error, surface, on-surface, surface-container-*, outline, background, on-background.
119Typography: display-lg/md/sm, headline-lg/md/sm, title-lg/md/sm, body-lg/md/sm, label-lg/md/sm.
120Rounded: none, xs, sm, md, lg, xl, full.
121 
122## CI Compatibility
123Chrome flags: `--headless=new --no-sandbox --disable-gpu --disable-dbus --use-gl=angle --use-angle=swiftshader`
124 
125## Defensive Code
126Retry with backoff (3 attempts, 1s/2s/4s), Timeout (30s page load, 10s pseudo-state), Graceful degradation (Tier 2 on empty extraction).
127 
128## Known Risks
129- DESIGN.md spec is alpha. Skill pins to current spec.
130- Puppeteer is heavy (~300MB Chrome). Document requirement clearly.
131- Prose quality depends on AI heuristics. grill-me is the validation gate.
132