Cloudflare Error 521: Web Server Down Checklist
Cloudflare error 521 means your origin web server refused the connection. This is not a Cloudflar...
Checklists for software errors, setup, and tool workflows.
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2. Isolate
3. Apply
4. Verify
Latest checklists
View listFix Git Clone Connection Timed Out Due to Proxy Settings
You run git clone https://github.com/example/repo.git and after a long pause you get...
Fix Chrome Access Violation Error When Opening PDFs
You click a PDF link in Chrome and instead of the document, you see an error: Access Violatio...
Fix Nginx Upstream Connection Refused in Proxy Pass
When Nginx returns a 502 Bad Gateway or logs upstream connection refused
Fixing Cloudflare Wildcard Subdomain Proxy Errors
If you've set up a wildcard DNS record (e.g., *.example.com) in Cloudflare and a...
Fixing Python Memory Errors When Generating Large Files
You're running a Python script that generates a large file—maybe a CSV with millions of rows ...
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