Websites can fail for dozens of reasons — from server overloads to SSL misconfigurations and CDN connectivity issues. This guide lists the most common website errors and links to step-by-step fixes.
Tip: Use Ctrl/Cmd + F to search for your error code (e.g., 521, 502, SSL).
Quick Checks (Before You Panic)
- Check if it’s only you: test from another device/network.
- Check uptime: your hosting panel, status page, or a basic uptime checker.
- Clear cache: browser cache, CDN cache, and WordPress cache (if applicable).
- Disable recent changes: last plugin/theme update, firewall rule, DNS change.
- Look at logs: server error logs, CDN firewall events, WordPress debug log.
Server Errors (HTTP 5xx)
Server errors mean the request reached your server, but the server couldn’t complete it. These often relate to hosting resources, misconfiguration, timeouts, or application crashes.
Most common 5xx errors
- 500 Internal Server Error — Generic server failure. Fix guide
- 501 Not Implemented — Server doesn’t support the request method/feature. Fix guide
- 502 Bad Gateway — Bad response from upstream (PHP-FPM, proxy, app). Fix guide
- 503 Service Unavailable — Server overloaded or in maintenance. Fix guide
- 504 Gateway Timeout — Upstream timeout (slow DB, API, heavy script). Fix guide
Fast fixes (try first)
- Restart web server / PHP service (if you manage the server).
- Disable the last plugin/theme update (WordPress) or rollback deployment.
- Increase timeouts or PHP memory limit (if relevant).
- Check server error logs for the exact failure message.
Client Errors (HTTP 4xx)
Client errors usually mean access issues, missing pages, or blocked requests. They can still be caused by server rules, WAF, or misconfigured permissions.
Common 4xx errors
- 400 Bad Request — Malformed request/cookies/headers. Fix guide
- 401 Unauthorized — Authentication required/failed. Fix guide
- 403 Forbidden — Permission or security rule blocks access. Fix guide
- 404 Not Found — Resource missing or wrong URL. Fix guide
- 429 Too Many Requests — Rate limit triggered. Fix guide
CDN & Security Errors
CDN errors often happen when the CDN can’t reach your origin server, your SSL mode is mismatched, or your firewall rules are blocking traffic.
Common CDN errors (Cloudflare-style)
- 520 Web Server Returned an Unknown Error — Origin sent an unexpected response. Fix guide
- 521 Web Server Is Down — CDN can’t connect to origin (server down or blocked). Fix guide
- 522 Connection Timed Out — Origin not responding in time. Fix guide
- 523 Origin Is Unreachable — DNS/IP routing issue to origin. Fix guide
- 524 A Timeout Occurred — Origin took too long to respond after connection. Fix guide
- 525 SSL Handshake Failed — TLS handshake failed between CDN and origin. Fix guide
- 526 Invalid SSL Certificate — Origin SSL invalid in strict mode. Fix guide
- 1020 Access Denied — Blocked by firewall rule/WAF. Fix guide
- 1015 Rate Limited — Request rate triggered protection. Fix guide
Fast fixes (try first)
- Confirm the origin server is online and reachable directly (bypass CDN).
- Whitelist CDN IP ranges in your firewall/security plugin.
- Check SSL mode (e.g., Full/Strict) matches your origin certificate.
- Review WAF/firewall events for blocked IPs and rules.
SSL/TLS Errors
SSL/TLS errors usually come from certificate issues, invalid chains, wrong hostname, outdated protocols, or mixed-content resources.
Common SSL/TLS problems
- SSL handshake failed — Protocol/cipher mismatch or blocked port 443. Fix guide
- Invalid SSL certificate — Expired, self-signed, or wrong domain. Fix guide
- ERR_SSL_PROTOCOL_ERROR — Bad TLS config or proxy issue. Fix guide
- Mixed content — HTTP resources on HTTPS page. Fix guide
- Certificate chain incomplete — Missing intermediate certificates. Fix guide
Fast fixes (try first)
- Renew/install a valid certificate for your exact domain.
- Install the full chain (intermediates).
- Force HTTPS and fix mixed-content URLs.
- Enable modern TLS (1.2/1.3) and ensure port 443 is open.
DNS Errors
DNS errors occur when the domain can’t resolve correctly to the server IP. They often happen after DNS changes, expired domains, wrong records, or propagation delays.
Common DNS errors
- DNS_PROBE_FINISHED_NXDOMAIN — Domain not found / missing DNS records. Fix guide
- DNS server not responding — Resolver issue or blocked DNS. Fix guide
- Too many redirects (can be DNS+SSL) — Misconfigured HTTPS or proxy. Fix guide
Fast fixes (try first)
- Check A/AAAA records point to the correct server IP.
- Check nameservers are correct at the registrar.
- Wait for propagation (can take hours) and clear local DNS cache.
- Verify domain is active and not expired.
WordPress Errors
WordPress errors are usually caused by plugins, themes, PHP limits, database issues, or caching conflicts. The fastest way to troubleshoot is to isolate changes and check logs.
Common WordPress issues
- White Screen of Death (WSOD) — Fatal PHP error or memory issue. Fix guide
- Error Establishing a Database Connection — DB down or wrong credentials. Fix guide
- 403 Forbidden (WordPress) — Permissions/WAF/hotlink rules. Fix guide
- Memory exhausted — PHP memory limit too low. Fix guide
- Critical error on this website — Plugin/theme conflict. Fix guide
Fast fixes (try first)
- Disable the last installed/updated plugin.
- Switch to a default theme to test theme conflicts.
- Increase PHP memory limit and check PHP version compatibility.
- Enable debugging and review the error log.
FAQ
Which errors should I fix first?
Start with errors that fully block access (5xx, 521/522/525/526, DB connection errors). Then handle performance and warnings (mixed content, redirect loops).
Why do these errors keep coming back?
Repeated errors usually indicate an underlying cause: unstable hosting resources, misconfigured SSL/CDN mode, aggressive firewall rules, or a WordPress plugin conflict. Fix the root cause, not just the symptom.
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