Reference
Stable, standardized facts you can rely on — with quick answers, limits, sources, and a path back to a useful tool.
What problems does this reference set solve?
Short answer: Use these pages when you need to confirm what a status code, port, or Unix permission actually means. Start with the definition and limits, then return to a tool for the conversion or inspection step.
HTTP Status Codes
Every common status code, what it means, and what to check when 502/503/504 hit.
Network Ports
The ports you actually meet — services, ranges, and security notes.
Unix Permissions
rwx, octal modes, and what 755 vs 644 vs 600 really allow.
Sources and verification
Definitions are checked against public standards and maintained technical documentation. The links are there so you can verify the facts behind each quick answer.