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/before-and-after

by Michael Shimelesmichaelshimeles/skills1.3k stars
200

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.

Use this Skill: https://skilld.dev/gh/michaelshimeles/skills/before-and-after

Nothing lands on disk. Nothing to clean up.

Fork this Skill

Edit a local copy. It keeps the author and licence.

SKILL.md

≈81 tokens for metadata: the name and description. ≈831 when used: this file.

Description uses 4.0% of example budget

Before choosing a Skill, your Agent reads its name and description. All available Skills share that space.

  • A shorter description leaves more room for other Skills. This entry exceeds our 1% size suggestion.

In our Claude Code example, all Skill names and descriptions share 8,000 characters. This Skill uses ≈324 characters, or 4.0%.

The 1% threshold is a size suggestion. Longer descriptions can still fit.

Your model, settings, and other Skills decide how much text your Agent can read.

Example settings and source

The example uses a 200k-token context and default Claude Code settings. The count includes the name, description, separators, and when_to_use when present. Codex also counts local file paths.

Skit's source and limits: Codex 0.160.1, Claude Code 2.1.292.

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
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:

  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

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

Source: SKILL.md on GitHub

Skill behaviors

skilld matched fixed text patterns in SKILL.md and file names. Patterns miss obfuscated code.

skilld run checks every file with the same patterns. It asks for approval before it loads a Skill with a behavior marked Needs approval.

Third-party checks

2 warnings1mo3 checks · Risk SAFE
  • Gen Agent Trust Hub1mo

    This skill allows for capturing and comparing visual changes to web pages, including uploading results to storage services and integrating them into GitHub Pull Requests. It uses official tools and follows standard development practices.

  • Socket1mo

    1 alert: gptAnomaly

  • Snyk1mo

    Risk: MEDIUM · 1 issue

Provenance

Signed by skilld. This ties the file your Agent reads to that commit on GitHub. It does not review the instructions.

Last checked against GitHub 3 weeks ago.

updated last month

Capability

What it can do
Runs commands
All 12 allowed tools
Bash(npx @vercel/before-and-after *)Bash(before-and-after *)Bash(which before-and-after)Bash(npm install -g @vercel/before-and-after)Bash(*/upload-and-copy.sh *)Bash(curl -s -o /dev/null -w *)Bash(gh pr view *)Bash(gh pr edit *)Bash(vercel inspect *)Bash(vercel whoami)Bash(which vercel)Bash(which gh)

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