HTTP 503 Through a Proxy: Check Retry-After, Overload, and Upstream Capacity
Diagnose HTTP 503 through a proxy by identifying the response owner, reading Retry-After correctly, comparing direct and proxied paths, reducing load, and bounding retries.
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HTTP 400 Through a Proxy: Check URL Encoding, Headers, and Request Bodies
Troubleshoot HTTP 400 through a proxy by identifying the response owner, comparing direct and proxied requests, and checking URL encoding, host headers, request bodies, and size limits.
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HTTP 401 Through a Proxy: Check WWW-Authenticate, Token Scope, and Redirects
Diagnose HTTP 401 responses through a proxy by separating target authentication from proxy authentication, then checking WWW-Authenticate, token scope, session expiry, redirects, and request headers.
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Proxy Redirect Loops: Trace Location Headers, Scheme Changes, and Session State
Diagnose proxy redirect loops by recording each Location header, scheme and host change, region decision, cache layer, and session-state dependency before changing exits.
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Proxy TLS Handshake Fails: Separate CONNECT, SNI, and Certificate Trust Errors
When a proxy TLS handshake fails, separate proxy tunnel setup from SNI, certificate chain, trust-store, TLS version, and client-library errors before replacing the exit.
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Proxy IP Changed but Requests Use the Old Exit: Keep-Alive and Connection Pool Checks
When a proxy IP changes but requests still use the old exit, inspect persistent connections, client pools, DNS state, and sticky assignment before rotating again.
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Proxy Authentication Setup: Username, Password, and IP Whitelist Checks Before Client Rollout
Proxy authentication setup should be verified before a client rollout. Use this checklist to separate username/password errors, IP whitelist gaps, protocol mismatch, and client-side configuration problems.
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Proxy Protocol Mismatch: Diagnose HTTP, HTTPS, and SOCKS5 Before Replacing IPs
A practical proxy protocol mismatch checklist for teams separating HTTP, HTTPS, SOCKS5, authentication, DNS mode, and client support problems from real IP quality issues.
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SOCKS5 Proxy Works in cURL but Fails in Python Clients
If the same SOCKS5 credentials work in cURL but fail in Python clients, check URL scheme, DNS mode, auth encoding, and library transport support before rotating IPs.
