visual-lint

name	visual-lint
version	0.1.1
description	Screenshot UI defect lint
allowed-tools	["Bash","Read","Write","Glob","Grep","AskUserQuestion","Agent"]

/visual-lint — Baseline-free rendered-UI defect detection

Codex Compatibility

When running this skill in Codex, translate Claude Code-only primitives before acting: AskUserQuestion -> chat/request_user_input, TodoWrite -> update_plan, Task/TaskCreate/TeamCreate/SendMessage -> spawn_agent/send_input/wait_agent when available and allowed, and EnterPlanMode/ExitPlanMode -> a concise chat plan plus explicit approval. Resolve Read/Write/Bash/WebSearch/WebFetch to Codex file/shell/web tools, and map ~/.claude/... paths to ~/.agents/... or ~/.codex/... unless the task explicitly targets Claude Code. The Agent-launched web-designer adjudicator maps to a Codex sub-agent spawn; if unavailable, run the rubric inline (lightweight mode).

Cursor Compatibility

When running this skill in Cursor Agent, translate Claude Code-only primitives before acting: AskUserQuestion -> AskQuestion; TodoWrite -> Cursor TodoWrite or an equivalent checklist; Task/Agent sub-agent flows -> Cursor Task (subagents), parallel Tasks, or run_in_background when allowed; EnterPlanMode/ExitPlanMode -> Plan mode (SwitchMode / CreatePlan) plus explicit user approval. Resolve Read/Write/Bash/web/search/MCP via Cursor Composer or Agent equivalents. MCP names written as mcp__server__tool typically map to call_mcp_tool. Map ~/.claude/... to ~/.cursor/skills/ unless the task explicitly targets Claude Code.

Screenshot a running app, run a structured defect rubric over the rendered pixels, and produce a findings report with cited evidence. Fixing is out of scope — this skill reports. Hand the report to a session that owns the source if the user wants the issues fixed.

Why this exists

lint and typecheck catch code-level problems the instant you save. But a whole class of bugs lives only in rendered pixels and is invisible to every static tool:

• A value readout 83% / 15px wraps onto two lines because a fixed-width span (w-14=56px) is narrower than its ~75px content. The code is type-correct and lint-clean — the breakage exists only on screen. (This skill's calibration fixture: references/fixtures/opacity-blur-wrap.png.)
• A label overflows its container at a narrow window width.
• Two elements overlap after a content change.
• A row's spacing drifts off the grid.

Today these get fixed only when a human notices and points them out. This skill codifies that human "that looks broken" judgment into a repeatable rubric so a model can catch it the way ESLint catches an unused variable.

Why VLM judgment, not a visual-regression tool: every mainstream visual-testing tool (Applitools, Percy, Chromatic, Playwright toHaveScreenshot) is a baseline-required regression detector — it diffs against a saved golden image and therefore cannot flag a first-occurrence bug. The goal here is to catch new breakage with no baseline, which only spec-driven geometry or vision-language-model judgment can do. v1 uses VLM judgment.

Where it sits among sibling skills:

Skill	Question it answers
Functional QA	Does it function? (clicks work, IPC fires, state persists)
/design-review	Is it aesthetically good? (hierarchy, polish, AI-slop) — and it fixes
/visual-lint	Is the render broken? (wrap, overflow, overlap, misalign) — read-only

Scope and non-goals

In scope (v1, pure-VLM): detecting display defects in the rendered pixels of a running app — unintended wrapping, truncation/clipping, element overlap, containment overflow, gross misalignment, off-grid spacing, broken/missing assets, contrast and target-size problems, theme/mode bleed, and state-dependent breakage (modal, hover, context menu, drag, scroll).

Out of scope:

• Fixing. This skill is read-only (see contract below). It reports.
• Aesthetic scoring / "is it beautiful". That's /design-review.
• Functional testing / "does it work". Use browser automation or manual QA separately.
• Sub-10px geometric precision (exact spacing rhythm, 1–3px offsets). VLMs are weak at this — it is explicitly deferred to Hybrid v2 (a deterministic getComputedStyle/getBoundingClientRect + axe-core + token-diff pre-pass that feeds the VLM bounded confirm/reject questions). v1 does not build that layer; for measurable claims the rubric reports "borderline — needs measurement", never a fabricated number.

🔒 Read-only contract (non-negotiable)

This skill MUST NOT:

• edit, format, or otherwise modify any source file,
• run git commit, git add, or any state-changing VCS command,
• run a code formatter, codemod, or autofix.

It MAY only: read source, drive the running app via playwright-cli, capture screenshots, and write a single report file under ./visual-lint-reports/. allowed-tools deliberately omits Edit to enforce this at the tool layer. If a user wants fixes, this skill's output is the input to a separate fixing session.

Required context before starting

Gather these; if any is missing and not inferable, ask once via AskUserQuestion:

1. Target — a running app reachable by playwright-cli. Default assumption: an Electron app exposing CDP on http://localhost:9222 (the skills-desktop convention: pnpm dev exposes it). For a web app, a URL + a browser context.
2. Scope — "whole app" vs a specific screen/flow ("Settings → Appearance").
3. Design source — auto-detect ./DESIGN.md in the target project. If present, project-aware mode activates (see references/design-system-criteria.md); if absent, fall back to the generic rubric. Do not ask — detect.

Executor: web-designer (primary) vs lightweight inline

Adjudication needs a vision-capable agent that reads the screenshots and applies the rubric. Two modes:

• Primary — web-designer subagent. Launch via the Agent tool (subagent_type: web-designer). It owns capture + judgment end-to-end, reading this skill's references/. Use it for a full pass: a professional design eye applies the DESIGN.md criteria most faithfully. This is the user's stated default.
• --lightweight — inline. The main Claude agent runs the same rubric itself (Claude is vision-capable; this was proven to catch the calibration fixture cleanly). No subagent spawn → faster and cheaper. Use for a quick single-screen check, when iterating, or when subagent overhead isn't worth it.

Same rubric, same report either way. If the user passes --lightweight, run inline; otherwise default to web-designer. (If the per-run subagent cost proves not worth it in practice, flipping the default to inline needs no code change.)

Workflow

Phase 0 — Preflight

1. Ensure no stale driver session: playwright-cli list; detach/kill-all if wedged.
2. Ensure the target app is running with its debug surface. For skills-desktop: kill-port 9222 if a prior pnpm dev died unclean, then pnpm dev.
3. Attach: playwright-cli attach --cdp=http://localhost:9222. All later commands use --s=default.
4. Detect ./DESIGN.md; note project-aware vs generic mode in the report header.

Phase 1 — State plan (present before capturing)

Derive the list of UI states to capture per references/ui-state-coverage.md: the always-on default-state full-window pass plus the five operation-path states (modal / context-menu / drag / scroll / hover) where reachable. Output a short per-screen state plan table before capturing so the run is auditable.

Phase 2 — Capture

For each planned state, capture a full-window screenshot via playwright-cli. Capture resolution caveat: playwright-cli hardcodes scale: 'css', so the PNG is 1× CSS resolution (~1400×941 on this app), not the 2× device pixels of a DPR-2 render — window.devicePixelRatio reports 2 but that does not change the captured file. For dense or borderline regions, take an element-scoped or CSS-zoom crop (see Capture recipes below) and re-judge from that. Re-snapshot after any DOM-mutating action — eN refs are valid only for the latest snapshot. Save shots under the report's screenshots/ dir.

Phase 3 — Adjudicate

Apply, in this order, against every screenshot:

1. references/anti-false-positive.md — the process rules that bound the judgment (describe-before-judge, cite-or-drop, enumeration-not-quota, low-confidence → question, adversarial self-check). Read this first; it governs everything.
2. references/defect-rubric.md — categories A–F. Each item is a direct verification prompt. Every finding uses the 4+1 scaffold: element · defect · expected_vs_actual · severity · confidence.
3. references/design-system-criteria.md — in project-aware mode, fold the DESIGN.md tokens in as perceptual checks (e.g. status-green must survive the neutral theme; no shadow on resting cards). In generic mode, skip the project-specific rows.

Phase 4 — Report

Emit templates/visual-lint-report.md to ./visual-lint-reports/{YYYYMMDD}-{scope}.md (screenshots in a sibling screenshots/ dir). Group findings by severity. End with the read-only footer. Then detach: playwright-cli --s=default detach (does not close the app).

Capture recipes (project-aware)

Electron (primary — skills-desktop CDP :9222):

playwright-cli list                                   # check for stale sessions
playwright-cli attach --cdp=http://localhost:9222     # attach once per run
playwright-cli --s=default snapshot                   # a11y tree with eN refs
playwright-cli --s=default screenshot --filename=./visual-lint-reports/<run>/screenshots/<state>.png
playwright-cli --s=default click e5                   # interact by ref from latest snapshot
playwright-cli --s=default fill e3 "text"
playwright-cli --s=default press Escape
playwright-cli --s=default eval 'window.devicePixelRatio'   # reports 2, but PNG stays 1× CSS (scale:css hardcoded) — NOT a resolution check
playwright-cli --s=default detach                     # leaves the app running

Web app (documented alternate): open a browser context to the URL instead of CDP attach; the screenshot/snapshot/interact verbs are otherwise identical. The rubric and report are capture-method-agnostic.

Calibration (dev-time, not per-run)

Two worked-example bugs anchor the rubric, each paired with an .expected.md target:

• references/fixtures/opacity-blur-wrap.png — the wrapping anchor: the 83% / 15px readout wraps onto two lines (severity 2, high confidence, citing both lines; rubric A1/A7, home B).
• references/fixtures/symlink-health-clip.png — the clipping anchor: the large 100% value in the "Symlink Health" card is sliced at the card's top content edge (severity 2–3, high confidence, citing the 100% value; rubric A3, home B1/B3).

When you change this skill's rubric, run it once against both PNGs and confirm each still emits its expected finding. A rubric edit that stops catching either fixture is a regression — fix it before shipping. This is a construction-time anchor; normal /visual-lint runs do not re-run it.

Pre-flight checklist

• Driver attached, no stale session, target app responsive.
• ./DESIGN.md detection resolved (project-aware vs generic noted in report).
• State plan table presented before capture.
• Screenshots full-window; dense/borderline regions have a zoom crop (captures are 1× CSS via playwright-cli, not 2× device px).
• Every finding cites a visible element (cite-or-drop honored).
• Report written under ./visual-lint-reports/; no source edits, no commits.
• Driver detached (app left running).

References

• references/defect-rubric.md — what to look for (categories A–F + finding scaffold).
• references/anti-false-positive.md — how to judge without hallucinating (read first).
• references/ui-state-coverage.md — which states to capture (default + 5 op paths).
• references/design-system-criteria.md — DESIGN.md tokens as perceptual checks.
• references/fixtures/opacity-blur-wrap.{png,expected.md} — wrapping calibration anchor.
• references/fixtures/symlink-health-clip.{png,expected.md} — clipping calibration anchor.
• templates/visual-lint-report.md — the read-only report skeleton.