How to Fix Cloudflare 521 Error (Port 443 Blocked)
When you see a Cloudflare 521 error, it means Cloudflare’s servers cannot connect to your origin ...
Checklists for software errors, setup, and tool workflows.
1. Reproduce
2. Isolate
3. Apply
4. Verify
Latest checklists
View listFix VS Code Source Control Not Detecting File Modifications
You edit a file, save it, but the Source Control panel in VS Code shows nothing. No pending chang...
Checklist to Fix npm Permission Denied Errors
If you see "EACCES: permission denied" or "Error: EACCES, mkdir" when running npm...
How to Fix Nginx 'Upstream Connection Refused' Error
When Nginx returns a 502 Bad Gateway with upstream connection refused in the error l...
How to Fix Cloudflare Error 521: Origin Server Unreachable
If you see Cloudflare error 521, your origin server is not responding to Cloudflare's request...
Fix Windows Update Error 0x800f081f After SFC ScanNow
You run sfc /scannow to check system files, and it completes successfully. But when ...
Topic paths
Quick titles
How to Activate Python Virtual Environment in Windows CMDResolve 521 Web Server Down with Firewall ChangesTroubleshooting VSCode Debugger for TypeScriptFix Windows Security App Blocked by AntivirusChrome Extension Conflict Fix for DNS ErrorsFix NET::ERR_CERT_AUTHORITY_INVALID on Windows 10How to Fix Chrome Crashing at Launch with RegistryNginx Upstream Not Found Error Fix