Articles & Guides
Useful resources for web developers and system administrators
SSL/TLS
Your Connection Is Not Private: Which of Six Errors It Is
The warning is identical for six unrelated faults. The code beneath it says whether the cause is your clock, your network, or the site's certificate.
Security
Cloudflare Error 1015: Why Your Own Visitors Are Rate Limited
Error 1015 is a rule you configured, firing. Find which one matched, check what it counts by, and stop it catching customers, mobile users and your monitoring.
SSL/TLS
ERR_CERT_COMMON_NAME_INVALID: Certificate Name Mismatch
Browsers stopped reading the Common Name in 2017 and match the SAN list instead. Print the names your certificate covers and fix the real mismatch in minutes.
Performance
Website Slow Abroad: Why Distance Multiplies Latency
A healthy server and a four-second load abroad are both real. Distance is paid on every round trip, and a first view spends four or five before any HTML lands.
HTTP
Nginx 499 Client Closed Request: What It Means and What to Fix
499 is a log entry, not a status code, and nobody ever receives one. The duration distribution splits timeout misconfiguration from a genuinely slow upstream.
HTTP
ERR_HTTP2_PROTOCOL_ERROR: Why It Is Almost Never Your Browser
Chrome aborts on an invalid HTTP/2 frame, so cache and browser tips miss the cause. One protocol comparison separates server, network and client in seconds.
Performance
Slow TTFB: How to Find the Stage That Is Actually Slow
TTFB is five stacked intervals, not one number. Split it with a single curl command, find the stage that dominates, and fix the cause instead of guessing.
SSL/TLS
TLS Works in the Browser but Fails in curl, Java and Python
A green padlock is not proof. Browsers repair a missing intermediate certificate silently while strict clients reject it. How to find and fix the real cause.
Networking
DNS, CDN, TLS or Origin: How to Isolate a Web Outage
A web request crosses five layers and each fails identically in a browser. Test them in order, one command per layer, and find the real cause in minutes.
DNS
Resolvers Return Different IPs: Propagation and Stale Cache
Two resolvers, two answers for one hostname. Four causes, only one fixes itself. Query each authoritative nameserver and tell propagation from a real defect.