Frequently Asked Questions
ErrorLookup FAQ
Quick answers for common troubleshooting, triage, and incident-response questions about HTTP status codes and network errors.
About ErrorLookup
How is ErrorLookup different from a status code table?
Each guide explains meaning, likely causes, first checks, deeper checks, remediation options, and closely related errors — not just a one-line definition. Guides are built for production debugging, not just academic reference.
Can I use ErrorLookup during a live production incident?
Yes. Start from the exact code or browser message, follow the first checks to isolate the layer (client, server, proxy, CDN, DNS/TLS), then use related guides and comparison pages to test alternatives before making changes.
Is ErrorLookup content available without JavaScript?
Yes. Core content, navigation, and all guide text are static HTML. Search uses JavaScript, but all guides, comparisons, and category pages are fully accessible without it.
Troubleshooting HTTP errors
What HTTP codes are most commonly confused?
The most commonly confused pairs are: 401 vs 403 (authentication vs authorization), 404 vs 410 (not found vs permanently removed), 301 vs 302 (permanent vs temporary redirect), and 502 vs 503 vs 504 (bad gateway vs unavailable vs timeout). The comparison pages are built specifically for these decisions.
What is the quickest way to separate 502, 503, and 504?
Classify the response type first: 502 means the upstream returned an invalid or unparseable response, 503 means the service is unavailable (overloaded or in maintenance), 504 means the upstream timed out without responding. Validate each with your proxy logs and origin logs before making changes.
Do Cloudflare 52x errors always mean the origin is down?
No. They indicate a problem between Cloudflare's edge and your origin, but the cause varies: routing issues, TLS negotiation failures, firewall rules blocking Cloudflare IP ranges, or upstream timeout mismatches. Each 52x error has a specific meaning — check the exact code before assuming the origin is down.
Are browser network errors the same as HTTP status codes?
No. Browser network errors like ERR_CONNECTION_REFUSED or ERR_NAME_NOT_RESOLVED occur before an HTTP response is received — the connection itself failed. DNS, TCP, and TLS diagnostics should come before HTTP-level checks when you see these.
Using the site
How do I find the right guide quickly?
Use the search (Ctrl+K or Cmd+K) to jump directly to any status code number, error name, or keyword. You can also browse by code number, browse by category, or use the comparison pages when you are deciding between two similar codes.
When should I use the comparison pages?
Use the comparisons when multiple plausible error codes match the same symptom and you need to distinguish them before touching the wrong layer. For example, if you are unsure whether to return 401 or 403 in a new API endpoint, the 401 vs 403 comparison covers semantics, caching, and client behavior side by side.
Explore more
Browse all status codes · In-depth guides · Comparison pages · About ErrorLookup