Web fix notes

Short, practical fixes for things that silently break on small sites. Written by Dimitry (9213651 Canada Inc.); each note discloses the paid tool I build for that problem, and every note works without it.

• State of share cards, icons and security headers (Oct 2026)
• og:image not showing on LinkedIn, Slack or Facebook: the 6 usual causes
• facebookexternalhit gets 403 but the page loads for me
• Gmail/Yahoo one-click unsubscribe: what the headers must look like (RFC 8058)
• Missing apple-touch-icon, manifest icons and favicon.ico: the minimal set
• Site migration: find every old URL that will 404 before launch
• Security headers on Vercel and Netlify: a safe baseline
• Block .env, .git and backup files on Apache and nginx
• llms.txt format: a minimal valid example
• Bookmarklets for checking the page you’re on