Before-After Screenshot Skill Skill

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)

Pre-flight — which before-and-after || npm install -g @vercel/before-and-after
Protection check — if .vercel.app URL: curl -s -o /dev/null -w "%{http_code}" "<url>" (401/403 = protected)
Capture — before-and-after "<before-url>" "<after-url>"
Upload — ./scripts/upload-and-copy.sh <before.png> <after.png> --markdown
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

| Flag | Description | |------|-------------| | -m, --mobile | Mobile viewport (375x812) | | -t, --tablet | Tablet viewport (768x1024) | | --size <WxH> | Custom viewport | | -f, --full | Full scrollable page | | -s, --selector | CSS selector to capture | | -o, --output | Output directory (default: ~/Downloads) | | --markdown | Upload 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:

Check Vercel CLI: which vercel && vercel whoami
If available: vercel inspect <url> to get bypass token
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

| Error | Fix | |-------|-----| | command not found | npm install -g @vercel/before-and-after | | could not determine executable | Use npx @vercel/before-and-after (full name) | | 401/403 on .vercel.app | See Vercel protection section | | Element not found | Verify selector exists on page |

Agent Skills: Before-After Screenshot Skill

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Skill Files