---

name: diff description: Reconcile a converted/built web page against its source prototype with two complementary probes — a PIXEL/layout diff (stretched images, dropped wraps, blank renders, colour flips) and a STRUCTURAL content+typography diff (dropped/mis-slotted headings, eyebrows, CTAs; rendered-face font forks). Stack-agnostic via profiles (eds | generic). Use after converting a prototype to EDS/AEM (the stardust deploy skill Step 10), or for any prototype↔build fidelity check; invocable as the stardust diff skill and from workflows. license: Apache-2.0 compatibility: Requires Node 22+, Playwright with Chromium resolvable from the project, playwright-cli on PATH, and the impeccable skill (github.com/pbakaus/impeccable) installed alongside stardust.

stardust:diff — prototype ↔ build reconcile

Two probes that compare a source prototype against a built page. They catch disjoint failure classes — run BOTH; either alone gives a false "looks fine".

Both are framework-agnostic Playwright probes that compare two rendered URLs by computed style + DOM (not pixels). All stack-specific language lives in a profile (--profile eds|generic); the comparison logic is generic.

When to use

• After converting a prototype to EDS (the stardust deploy skill's Step 10) — use --profile eds.
• Any "does the build match the design?" check between two rendered URLs (a Figma export vs a React build, a legacy page vs a rebuild) — use --profile generic.
• Inside a conversion/QA workflow as the validation gate (see Workflow use).

Not for: a single static file with no JS decoration (use the build/harness URL so components are decorated — a raw .plain.html has no roles to classify).

The two probes

Probe	Script	Sees	Blind to
Pixel / layout	skills/diff/scripts/visual-diff.mjs	stretched images, dropped max-width wraps, blank renders, surface/ground colour flips, image-count gaps	"right text, wrong slot"; a dropped CTA (full pixels, plausible colours → no flag)
Structural content + type	skills/diff/scripts/content-diff.mjs	MISSING / ROLE-SWAPPED headings·eyebrows·CTAs, invented/dropped body copy, rendered-FACE font forks (width probe); dropped placeholder/aria-label/title values, missing/wrong/moved icons — on the main root AND the header/footer chrome roots by default	geometry / layout regressions

content-diff extracts an ordered, role-classified inventory (heading / eyebrow / cta+href / body) from each root — the --main root(s) plus, by default, the header and footer chrome roots — classifying by computed style + tag so the prototype's DOM and the built DOM compare symmetrically, then diffs them root by root; a second inventory per root carries the placeholder / aria-label / title values and the icons.

Run it

# Prereq 0: playwright importable from the project root (node -e "import('playwright')"), else
# npm i -D playwright pixelmatch pngjs cheerio --legacy-peer-deps, never --no-save (extract
# SKILL.md § Setup). Run the copied scripts from the project root: ESM resolves from the script.
# Copy the WHOLE skills/diff/scripts/ dir: content-diff imports its local diff-profiles.mjs
# AND content-inventory.mjs (deploy keeps its own synced copies for #93/#94).
# Prereq: a RENDERABLE source. Static → serve from its own dir (python3 -m http.server).
# The build URL must be the DECORATED page (live/preview or a local harness), not raw markup.
# ONE server, ONE port — probe before starting one (curl is always present, lsof is not):
curl -sI localhost:8791/ | head -1                   # 200/404 = something serves the port; no line = free
curl -sI localhost:8791/<prototype>.html | head -1   # 200 = it serves YOUR dir: reuse it
command -v lsof >/dev/null && lsof -nP -iTCP:8791 -sTCP:LISTEN   # optional: names the pid
# Nothing answered → start yours. A foreign server: never kill it; use a per-project port
# (the traps: ../deploy/SKILL.md § Step 10).
PROTO="http://localhost:8791/<prototype>.html"
BUILD="https://<branch>--<repo>--<owner>.aem.page/<path>"   # or http://localhost:3000/<harness>

# 1. PIXEL/layout
node skills/diff/scripts/visual-diff.mjs   "$PROTO" "$BUILD" --profile eds --sections ".hero"

# 2. STRUCTURAL content + type
node skills/diff/scripts/content-diff.mjs  "$PROTO" "$BUILD" --profile eds   # --json dumps both inventories

Flags (both tools): --profile eds|generic (default eds), --width <px> (default 1280), --main <selector[,selector…]> (content root; content-diff defaults from the profile and takes a comma-separated list — every root is inventoried and diffed on its own and each finding line carries its root as [root]; visual-diff takes one selector, default main), content-diff only: --chrome / --no-chrome (default on — the header and footer roots, resolved as the first <header>/[role=banner] and <footer>/[role=contentinfo] outside the main root(s), are compared beside it; a side lacking one is measured as empty there and the root line says so), plus the live-target set (shared engine: scripts/live-session.mjs — every context sends the real-Chrome UA and the standard Chrome request headers; the UA alone still 403s on Akamai-class bot management):

• --ua <string> — user agent override (default: real-Chrome desktop UA).

• --wait-until <state> — goto wait override. Default rule (one shared defaultWaitUntil in scripts/live-session.mjs), decided per URL side, three tiers:

  • localhost/127.0.0.1 → networkidle (local prototypes / harnesses, unchanged);
  • EDS build/preview origins — hostnames ending in .aem.page, .aem.live, .hlx.page, .hlx.live → networkidle (they decorate asynchronously and reliably reach networkidle; measuring at domcontentloaded reads the pre-decoration DOM — flaky false reds / FONT FORK on deploy Step 10);
  • all other live http(s) → domcontentloaded (live sites with analytics beacons never reach networkidle).

  --wait-until overrides all three tiers.

• --dismiss [sel,...] — dismiss overlays on both sides: cookie consent (clicked, not removed) AND timed marketing/newsletter modals, plus optional extra site-specific selectors; the mouse is parked afterwards.

• --headed — escalation for bot-managed sites: headed stealth real Chrome.

• --locale <tag> — pin Accept-Language + context locale (geo-redirecting sites capture a different locale per run otherwise).

visual-diff also: --out <dir>, --sections a,b (per-section screenshots).

A bot-management challenge/blocked interstitial on either navigation fails LOUD with exit 3 — it is never measured as the source. Escalate with --headed; if that is still blocked, the site needs crawl.mjs-class capture and the check cannot run headless.

A plain (non-challenge) HTTP error on either side — e.g. a 404 build side, normal on aem.page before preview propagation — is NOT fatal: the probe logs a loud warning, measures the error page, and the flags (BLANK RENDER / content asymmetry) carry the signal with exit 0. That is the probes' advisory contract: 0 = ran (flags advisory), 1 = probe error, 3 = bot challenge.

The published-origin probes (#125)

content-diff reconciles a prototype with its build; against a LIVE commerce origin its per-node findings were false, and the pixel gate passed a page whose every card was clipped (../replica/reference/source-fidelity-gate.md § The all-pages published-origin gate). Three probes ask the checkable questions; all load both sides in the same window-free real-Chrome tier and settle them the same way (scripts/measure-live.mjs).

ORIGIN="https://www.example.com/<path>"; SERVED="https://main--repo--owner.aem.live/<path>"
node stardust/scripts/diff/clip-probe.mjs "$SERVED" [--json clip.json]                       # D1: exit 2 on cut / hidden text or controls
node stardust/scripts/diff/content-presence.mjs "$ORIGIN" "$SERVED" [--variable "<selO>=<selE>"]  # D2: exit 2 on MISSING/HIDDEN link or heading
node stardust/scripts/diff/unit-geometry.mjs "$ORIGIN" "$SERVED" --unit "<selO>=<selE>" --n 2      # D3: exit 2 on an element off / hidden / missing

Reading: a 🔴 clip group names the clipper (a fixed-height box with overflow: hidden) — fix that block's CSS, never the content. HIDDEN LINK = in the DOM but clipped (CSS); MISSING LINK = not served (encoder); CONTROL STATE = same control, another value; COUNT … = session-variable region, confirm by eye. The origin side fails loud on HTTP ≥ 400 (exit 4) and a bot challenge (exit 3). Traps: an infinite-scroll origin keeps loading under the settle — mark the region --variable; a live origin without <main> compares whole page against whole page (the scope line says so), header / footer left to the chrome crop gate unless --chrome; the count-phrase and "read more" heuristics are English word lists (--count-words, --more-words).

The header contract (#132)

Every probe above sees the header at rest (pointer parked, motion frozen), so it passes with every menu wrong; runs shipped boilerplate click dropdowns for hover mega menus, search and cart as plain links, a static list for a drill-down drawer. The header's behaviour is recorded from the source once and the build compared with it:

node stardust/scripts/diff/chrome-explore.mjs "$ORIGIN" stardust/chrome/header-contract.json   # 1440 + 390
node stardust/scripts/diff/chrome-explore.mjs "$SERVED" stardust/chrome/header-build.json
node stardust/scripts/diff/chrome-compare.mjs stardust/chrome/header-contract.json stardust/chrome/header-build.json \
  --profile replica --json stardust/chrome/header-parity.json    # functional under redesign and reskin

The explorer hovers (desktop), clicks and keys every header control and records each opened state (links, headings, crop, aria-expanded, focus, scroll lock, motion, close paths), nested levels within --max-states 400 --max-depth 4, search typeahead and submit, and the header scrolled; its summary line sizes the work. The comparer exits 2 on a missing control or state (hover rebuilt as click included), panel links, keyboard, close paths or scroll lock; replica adds open-state crops (2 %), motion (max(80 ms, 25 %)) and scroll states. Only the site owner clears a finding: stardust/chrome/header-decisions.json ({ decisions: [{ finding, decision, reason, by, at }] }), never signed by an agent. It runs at extract --prep (the contract), on the foundation shell and in deploy Step 10, on the live host before handover (done-check header_parity), and in qa. Crops stay in stardust/.work/chrome/.

Reading content-diff

• 🔴 MISSING CTA / HEADING / EYEBROW — real dropped content. FIX. A missing eyebrow is most often a segmentation drop where the eyebrow precedes its heading; a missing CTA means the component never rendered the link. These are exactly what the pixel probe cannot see.
• 🔴 ROLE SWAP — same text under a different role (body painted as eyebrow, eyebrow folded into a teaser). FIX the component's node segmentation.
• 🔴 MISSING PLACEHOLDER / ARIA-LABEL, MISSING ICON, ICON DIFF on an interactive element (an input, a button, a link or inside one) — a dropped localized search placeholder, a share link without its aria-label or icon, a wrong flag in a locale link, an empty icon box. FIX. Outside interactive elements the same findings are 🟡.
• 🟡 MISSING TITLE — always 🟡: a title tooltip is not read by most assistive tech and is commonly dropped by design. 🟡 ICON MOVED — the same icon (glyph code point / file name / svg signature) at another anchor, paired by identity and document order after the anchor passes (typically a text-less <button> host that anchors as button#n): the icon is present, CONFIRM its placement. 🟡 ICON KIND (glyph vs svg vs image — the pixel probe judges) and every EXTRA.
• Every finding line names its root — 🔴 MISSING PLACEHOLDER [header]: … — and the report prints one block per root (root "main", root "header", …; a root a side lacks is measured as empty there and the line says which side).
• 🟡 MISSING BODY / EXTRA — body prose dropped, or build copy with no source. Usually a placeholder→real-copy rewrite. CONFIRM intended; don't blindly "fix".
• 🟠 FONT FORK — matched lines whose rendered FACE differs (width probe, never document.fonts.check). source X→sys means the prototype named font X but never loaded it and fell back to system — the build self-hosting the intended fallback is then CORRECT, not a bug. All forked lines are grouped into one advisory.
• Known limitation — node-granularity JOIN/SPLIT reads as 🔴 (#87). When the source renders one text run as N sibling nodes and the build renders the same text as ONE node (or vice versa — e.g. three fact chips vs one combined chip span), the diff currently reports MISSING + ROLE SWAP + EXTRA for what is a non-defect. Until concat-matching lands (a source node that is a substring of a same-region build node → 🟡 JOIN/SPLIT advisory), verify a 🔴 whose texts concatenate into an EXTRA finding's text before treating it as dropped content — confirmed-justified is a pass.

Pass bar: visual red flags none/justified AND content-diff 0 structural 🔴 (🟡/🟠 confirmed intended). Re-run BOTH after each fix.

Profiles

skills/diff/scripts/diff-profiles.mjs holds them. A profile supplies the source/target labels, per-flag remediation hints, the font-delta threshold, the default content-root selector, and the eyebrow classifier thresholds. The engines carry no stack strings.

• eds (default) — Edge Delivery / DA remediation language + the stardust deploy skill's finding numbers.
• generic — neutral source/build language for any stack.

Add a profile by copying generic in diff-profiles.mjs and editing hints.

Shared engine + the in-loop sibling

The structural probe's classifier + differ live in skills/diff/scripts/content-inventory.mjs (deploy imports its synced copy). They measure with the same instrument as two gates of the stardust deploy skill: section-schema.mjs (the pre-code ENCODE/DECODE contract, deploy #93) and block-roundtrip.mjs (the in-loop per-block gate, deploy #94 — the same inventory diff, run per block at authoring time against a local decorate() harness, no DA needed, exit-code gated). Run the in-loop gate while converting; run THIS skill's two probes as the final post-deploy proof. A defect first found here that the in-loop gate passed = the delivery pipeline reshaped the content in transport — fix the block's flattened-shape fallback, not the authoring.

Workflow use

Call both scripts in a validation phase and gate on the output, as deploy's Validate phase does on a served, decorated build (local harness or branch preview): fix visual-diff's STRETCHED/FLUSH-LEFT/SURFACE-GROUND/GAP flags (unless justified) and every content-diff 🔴, confirm 🟡/🟠, loop until both are clean.