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vijpatel7vijpatel7/favorite_skills_and_plugins/.agents/skills/before-and-after/SKILL.md

before-and-after

Skill0 starsChanged 9 months agoMITView on GitHub

Captures before/after screenshots of web pages or elements for visual comparison. Use when user says "take before and after", "screenshot comparison", "visual diff", "PR screenshots", "compare old and new", or needs to document UI changes. Accepts two URLs (file://, http://, https://) or two image paths.

  • Installs packages

We split this skill into the rules it gives an agent

9 rules. 0 are common, 2 are distinctive, and 7 are very specific to this project.

  • 0

    Common

    Most of the 9 edited versions we read keep these.

  • 2

    Distinctive

    This author's own choices. Worth a look.

  • 7

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Use --full unless user explicitly asks for full page / full scroll capture

    line 28
  2. Very specific:

    Use --markdown when user wants PR integration or markdown output

    line 31
  3. Very specific:

    Use --mobile / --tablet if user mentions phone, mobile, tablet, responsive, etc.

    line 32
  4. Distinctive:

    If user provides only one URL or says "PR screenshots" without URLs, ASK: "What URL should I use for the 'before' state?

    line 34
  5. Very specific:

    If .vercel.app URL returns 401/403:

    line 93
  6. Very specific:

    Check Vercel CLI: which vercel && vercel whoami

    line 95
  7. Very specific:

    If available: vercel inspect <url> to get bypass token

    line 96
  8. Distinctive:

    If not: Tell user to provide bypass token, take manual screenshots, or disable protection

    line 97
  9. Very specific:

    If no gh CLI: output markdown and tell user to paste manually.

    line 115

“Common” is measured: kept by at least 6 in 10 of the 9 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Before-After Screenshot Skill

Package: @vercel/before-and-after Never use before-and-after (wrong package).

Agent Behavior Rules

DO NOT:

  • Switch git branches, stash changes, start dev servers, or assume what "before" is
  • Use --full unless user explicitly asks for full page / full scroll capture

DO:

  • Use --markdown when user wants PR integration or markdown output
  • Use --mobile / --tablet if user mentions phone, mobile, tablet, responsive, etc.
  • Assume current state is After
  • If user provides only one URL or says "PR screenshots" without URLs, ASK: "What URL should I use for the 'before' state? (production URL, preview deployment, or another local port)"

Execution Order (MUST follow)

  1. Pre-flight — which before-and-after || npm install -g @vercel/before-and-after
  2. Protection check — if .vercel.app URL: curl -s -o /dev/null -w "%{http_code}" "<url>" (401/403 = protected)
  3. Capture — before-and-after "<before-url>" "<after-url>"
  4. Upload — ./scripts/upload-and-copy.sh <before.png> <after.png> --markdown
  5. PR integration — optionally gh pr edit to append markdown

Never skip steps 1-2.

Quick Reference

# Basic usage
before-and-after <before-url> <after-url>

# With selector
before-and-after url1 url2 ".hero-section"

# Different selectors for each
before-and-after url1 url2 ".old-card" ".new-card"

# Viewports
before-and-after url1 url2 --mobile    # 375x812
before-and-after url1 url2 --tablet    # 768x1024
before-and-after url1 url2 --full      # full scroll

# From existing images
before-and-after before.png after.png --markdown

# Via npx (use full package name!)
npx @vercel/before-and-after url1 url2
FlagDescription
-m, --mobileMobile viewport (375x812)
-t, --tabletTablet viewport (768x1024)
--size <WxH>Custom viewport
-f, --fullFull scrollable page
-s, --selectorCSS selector to capture
-o, --outputOutput directory (default: ~/Downloads)
--markdownUpload images & output markdown table
--upload-url <url>Custom upload endpoint (default: 0x0.st)

Image Upload

# Default (0x0.st - no signup needed)
./scripts/upload-and-copy.sh before.png after.png --markdown

# GitHub Gist
IMAGE_ADAPTER=gist ./scripts/upload-and-copy.sh before.png after.png --markdown

Vercel Deployment Protection

If .vercel.app URL returns 401/403:

  1. Check Vercel CLI: which vercel && vercel whoami
  2. If available: vercel inspect <url> to get bypass token
  3. If not: Tell user to provide bypass token, take manual screenshots, or disable protection

PR Integration

# Check for gh CLI
which gh

# Get current PR
gh pr view --json number,body

# Append screenshots to PR body
gh pr edit <number> --body "<existing-body>

## Before and After
<generated-markdown>"

If no gh CLI: output markdown and tell user to paste manually.

Error Reference

ErrorFix
command not foundnpm install -g @vercel/before-and-after
could not determine executableUse npx @vercel/before-and-after (full name)
401/403 on .vercel.appSee Vercel protection section
Element not foundVerify selector exists on page

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