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Skillspixel-perfect

pixel-perfect

Testing & quality

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Updated 10-16 07:23

About this skill

Pixel Perfect

Note: Use pixel-perfect by default (free); use visual-regression-tester when you need hosted Chromatic integration.

Step 1: Check State

Run all three commands, then use the table to choose your workflow.


ls playwright.config.ts 2>/dev/null && echo "CONFIG_EXISTS" || echo "CONFIG_MISSING"
find snapshots/ -name "*.png" 2>/dev/null | head -1 | grep -q . && echo "BASELINES_EXIST" || echo "BASELINES_MISSING"
curl -s -o /dev/null -w "%{http_code}" --max-time 5 http://<app-host>:<port> 2>/dev/null | grep -q "^2" && echo "SERVER_OK" || echo "NO_SERVER"

If your dev server runs on a port other than 3000, adjust the URL in the curl command above.

Config Baselines Server → Do this
CONFIG_MISSING any any → Workflow A (Full Setup)
CONFIG_EXISTS BASELINES_MISSING SERVER_OK → Workflow B (Capture Baseline)
CONFIG_EXISTS BASELINES_EXIST SERVER_OK Run npx playwright test. If all tests pass ✓, done. If tests fail → see Step 2.
CONFIG_EXISTS BASELINES_EXIST NO_SERVER STOP. Tell the user: "Dev server is not running. Start it first, then re-check."
CONFIG_EXISTS BASELINES_MISSING NO_SERVER STOP. Tell the user: "No baselines and no dev server. Start the server first."

Do not guess the next step — use the table.

Step 2: If Tests Fail

Only consult this section after running npx playwright test and seeing a failure.

What kind of failure?
│
├─ "screenshot doesn't match" / snapshot diff
│ │
│ │ STOP. Ask the user:
│ │ "Was this visual change intentional (design update) or unexpected (possible bug)?"
│ │ Wait for an explicit answer — do NOT infer from context.
│ │ If the answer is ambiguous, ask again: "Please answer 'intentional' or 'bug'."
│ │
│ ├─ "Intentional" → Workflow C: Update Baseline
│ └─ "Bug" / "Unexpected" → Workflow D: Debug Comparison
│
├─ Tests flaky (pass sometimes, fail sometimes)
│ └─ → Workflow E: Fix Flakiness with Fixture
│
└─ Config errors / tests won't run
  └─ Check Node.js version (v18+), re-run `npx playwright install chromium`

Workflow A: Full Setup

Precondition: Step 1 returned CONFIG_MISSING. Exit condition: npx playwright test --list prints test names without errors.

Step 1. Check for existing package.json:

ls package.json 2>/dev/null && echo "EXISTS" || echo "MISSING"

If MISSING: run npm init -y first. If EXISTS: skip — do not re-initialize.

Step 2. Install Playwright:

npm install -D @playwright/test
npx playwright install chromium

If this fails: check node -v — requires v18+.

Step 3. Ask the user: "What URL does your dev server run on? (e.g. http://:)" Wait for their answer. Save it — you will use it in Step 4 and in Workflow B.

Step 4. Write the config file. Use the Read tool to load the template:

Read file: references/examples/playwright.config.ts Write it to: ./playwright.config.ts

If the user's URL differs from http://<app-host>:<port>, use the Edit tool to find the exact string 'http://<app-host>:<port>' inside playwright.config.ts and replace it with the user's URL.

Step 5. Write the test file:

Read file: references/examples/visual.spec.ts Write it to: ./tests/visual.spec.ts

Step 6. Verify setup is functional:

npx playwright test --list

If this errors or prints 0 tests: show the output to the user and stop. Do not proceed to Workflow B.

Optional: If the project uses custom fonts, JS animations (GSAP, Framer Motion), or lazy-loaded images, also install the fixture now — see Workflow E Steps 1–2.

Workflow A complete → continue to Workflow B.

Workflow B: Capture Baseline

Precondition: CONFIG_EXISTS + BASELINES_MISSING + SERVER_OK. (Or: just completed Workflow A.) Exit condition: find snapshots/ -name "*.png" | wc -l prints a non-zero number and snapshots are committed to git.

Step 1. Verify the dev server responds. Use the baseURL from playwright.config.ts (default: http://<app-host>:<port>). Replace the URL in the command if yours differs:

curl -s -o /dev/null -w "%{http_code}" http://<app-host>:<port>

Expected: 200. If not 200: STOP. Tell the user the server is not responding and ask them to start it.

Step 2. Check if Docker is available:

docker --version 2>/dev/null && echo "DOCKER_OK" || echo "NO_DOCKER"

If DOCKER_OK — capture inside Docker (matches Linux CI, avoids font rendering diffs):

docker run --rm --ipc=host -v "$(pwd):/work" -w /work \
mcr.microsoft.com/playwright:v1.50.1-noble \
npx playwright test --update-snapshots

If NO_DOCKER — ask the user:

"Docker is not available. Baselines captured locally on macOS can cause false CI failures due to font rendering differences. Do you want to proceed locally (acceptable if you won't use CI), or install Docker first?"

Wait for their answer before proceeding. If they confirm local: run npx playwright test --update-snapshots.

Step 3. Verify snapshots were created:

find snapshots/ -name "*.png" | wc -l

If output is 0 or command errors: STOP. Show the user the test output and ask to debug.

Step 4. Commit baselines:

if ! git rev-parse --is-inside-work-tree 2>/dev/null; then echo "Not a git repository — skipping commit."
elif git check-ignore -q snapshots/ 2>/dev/null; then echo "⚠ snapshots/ is listed in .gitignore — remove it so baselines can be committed."
else git add snapshots/
if git diff --staged --quiet; then echo "Snapshots already committed — nothing to add." else git commit -m "chore: add visual baselines"
echo "Done. Push to remote: git push"
fi
fi

Workflow B complete. Baselines are now the source of truth.

Workflow C: Update Baseline

Precondition: Tests failing with 'screenshot doesn't match' and the user confirmed the change is intentional. Use when a design change is intentional and the current baseline is outdated.

Before Step 1. Ask the user:

"What is the reason for updating these baselines? (e.g., 'updated button design', 'new header font')"

Wait for their answer. Save it. You will use it in Step 2. Do not proceed until you have a clear answer.

Step 1. Check if Docker is available:

docker --version 2>/dev/null && echo "DOCKER_OK" || echo "NO_DOCKER"

If DOCKER_OK — update snapshots inside Docker:

docker run --rm --ipc=host -v "$(pwd):/work" -w /work \
mcr.microsoft.com/playwright:v1.50.1-noble \
npx playwright test --update-snapshots

This updates all existing baselines AND creates new ones. If NO_DOCKER — existing baselines need updating, so local font rendering on macOS may differ from Linux CI:

  1. Install Docker (recommended) and rerun this step.
  2. Or run npx playwright test --update-snapshots locally and accept that CI may need a re-run after push (CI captures its own Linux baselines). Ask the user which they prefer before proceeding.

Step 2. Commit with the reason the user gave you:

git add snapshots/ && git commit -m "chore: update visual baselines — USER_REASON"

Replace USER_REASON with the exact answer from the user. Do not invent a reason. If the user's reason contains backticks, $(, or newlines, ask for a simpler version — those characters cause shell injection in the commit command.

⚠ Never auto-update snapshots in CI. Use the update-snapshots workflow for intentional updates — it requires a reason and commits with attribution.

Workflow D: Debug Comparison

Precondition: Tests failing with 'screenshot doesn't match' and the user confirmed it is a bug (unexpected change).

Step 1. Run tests and capture output:

npx playwright test 2>&1 | tail -30

Step 2. Find diff images (CLI-friendly — no browser needed):

find playwright-report/ -name "*-diff.png" -o -name "*-actual.png" 2>/dev/null | head -20
find test-results/ -name "*.png" 2>/dev/null | head -20

Show the user the list of diff image paths. Ask them to open the files to see what changed.

Step 3. If the user has a browser available, they can run the HTML report themselves:

npx playwright show-report

Do NOT run show-report yourself — it starts a web server and blocks the terminal indefinitely.

Workflow E: Fix Flakiness with Fixture

Precondition: Tests are flaky (pass sometimes, fail sometimes) — not a consistent snapshot mismatch. For pages with custom fonts, JS animations (Framer Motion, GSAP), or lazy-loaded images.

Step 1. Copy fixture to your project using the Read and Write tools:

Read file: references/fixtures/visual.ts Write it to: ./tests/fixtures/visual.ts

Step 2. In your test file (e.g. tests/visual.spec.ts), find the import line:

import { test, expect } from '@playwright/test';

Replace it with:

import { test, expect, waitForPageReady } from './fixtures/visual';

(Adjust the relative path if your test file is in a different location.)

Step 3. In every test that calls toHaveScreenshot(), add these two lines immediately before the toHaveScreenshot call:

await page.locator('TODO_REPLACE_WITH_KEY_SELECTOR').waitFor(); // key element confirming page is loaded (e.g. 'h1', '.hero', '[data-testid="loaded"]')
await waitForPageReady(page); // fonts + images + GSAP freeze

Replace TODO_REPLACE_WITH_KEY_SELECTOR with the actual selector for the main content element on that page. The fixture uses addInitScript (runs before any app JS) to:

  • Mock IntersectionObserver (lazy loaders fire immediately)
  • Set window.__PLAYWRIGHT__ = true (for Framer Motion / app-level animation disabling)

Workflow F: GitHub Actions

Precondition: Workflow B is complete — baselines are committed and pushed to git. Exit condition: Both workflow files exist at .github/workflows/visual-tests.yml and .github/workflows/update-snapshots.yml, and CI runs green on push.

Step 1. Read and write the workflow files:

Read file: .github/workflows/visual-tests.yml Write it to: ./.github/workflows/visual-tests.yml

Read file: .github/workflows/update-snapshots.yml Write it to: ./.github/workflows/update-snapshots.yml

Step 2. Configure BASE_URL for CI. Ask the user:

"What URL should CI run visual tests against? (e.g. https://staging.example.com)"

Then add it as a repository secret in GitHub (Settings → Secrets and variables → Actions → New repository secret, name: BASE_URL). The workflows already read BASE_URL from secrets — no edits needed. If the user has no staging URL yet (tests run against a local app host only), skip this step. CI will fail at the network step until a server is available.

Key requirements:

  • Baselines must be committed to git before running in CI
  • CI=true is set automatically by GitHub Actions
  • Both workflows use --ipc=host to prevent Chromium crashes in Docker
  • update-snapshots.yml runs only on branches, never on tags (prevents corrupting release tags)
  • ⚠ Keep the Docker image version in sync with @playwright/test in package.json. To check: node -e "console.log(require('./package-lock.json').packages['node_modules/@playwright/test'].version)"

Key Options

Option Default Use
maxDiffPixelRatio 0.01 % pixels allowed to differ (0.01 = 1%). Set to 0 for zero tolerance
threshold 0.05 Per-pixel color sensitivity (0–1). Raise to 0.1 only for font anti-aliasing false positives
reducedMotion 'reduce' Sets prefers-reduced-motion CSS media query. Remove if you want to test the default (animated) visual state
mask [] Locators to black out (prices, timestamps, live data)
fullPage false Capture entire scrollable page
animations 'disabled' Default — CSS + Web Animations API stopped at screenshot time

Quick Commands

npx playwright test # compare vs baseline
npx playwright test --project=Desktop # specific viewport
npx playwright test tests/visual.spec.ts # specific file
npx playwright test --update-snapshots # update changed baselines
npx playwright test --update-snapshots=missing # only add new baselines