Articles & Guides
Useful resources for web developers and system administrators
Networking
ERR_FAILED (net::ERR_FAILED) in Chrome: Causes and Fixes
net::ERR_FAILED (-2) is Chrome's generic network error. The cause is usually on your side: a proxy or PAC file, an extension, antivirus, site data.
Domains
Domain Owner Lookup: Who Owns a Domain, Its Age and History
How to find who owns a domain with WHOIS and RDAP, what GDPR redaction hides, how to reach a private owner, and how to read domain age, registrar and history.
DNS
DNS Server Not Responding: How to Fix It on Windows and More
DNS server not responding? Find the cause by symptom and fix it: router reboot, flushdns, Winsock reset, public DNS like 1.1.1.1, nslookup tests, macOS and Linux.
SSL/TLS
Your Connection Is Not Private: What It Means and How to Fix It
“Your connection is not private” explained: what each NET::ERR_CERT code means, how to fix it on your device or server, and when it is safe to proceed.
HTTP
Cloudflare Error 524 A Timeout Occurred: Causes and Fixes
Error 524 means your origin accepted Cloudflare's connection but sent no response within 125 seconds. Find the slow request, fix it, and compare codes 520–526.
Tools
How to Clear Browser Cache: Chrome, Safari, Firefox, Edge
Clear your browser cache in Chrome, Safari, Firefox and Edge: shortcuts, hard reload, one-site data, SSL and DNS caches, plus when clearing won't help.
Security
Check a File for Viruses Online: Scanners, Hashes, Reports
How to check a file for viruses online: VirusTotal, OpenTIP, MetaDefender, SHA-256 lookups without uploading, reading detections and scanning files over 1 GB.
SSL/TLS
Russian Trusted Root CA: why browsers reject it and how to install
Russian bank sites fail in Chrome, Safari and Firefox: the Ministry root is in no trust store. How to install it per platform, and what trusting a root means.
Networking
How to Test a Mail Server: SMTP, TLS, Relay and PTR
How to test a mail server: the SMTP greeting, STARTTLS support, open relay, the PTR record and blocklists. Five checks with commands and what each finding means.
DNS
Cloudflare 1.1.1.1 IPv6 DNS: 2606:4700:4700::1111 and Setup
Cloudflare DNS: IPv4 1.1.1.1 and 1.0.0.1, IPv6 2606:4700:4700::1111 and ::1001, filtered 1.1.1.2 and 1.1.1.3, DoH and DoT. Setup and fixes.