Articles & Guides
Useful resources for web developers and system administrators
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 DNS 1.1.1.1: All Addresses, Setup and Why It Fails
Cloudflare DNS 1.1.1.1 explained: the alternate 1.0.0.1 and filtered pairs, DoT hostname and DoH URL, setup on every device, and why 1.1.1.1 gets blocked.
DNS
AdGuard DNS: Addresses, Setup and What It Actually Blocks
AdGuard DNS addresses for all three modes, setup on a router, Windows, macOS and Android, plus DoH, DoT and DoQ. What a DNS filter blocks and what it never can.
DNS
Quad9 DNS 9.9.9.9: What It Is, Setup and How It Compares
Quad9 (9.9.9.9) is a public DNS resolver that blocks malicious domains. The .9, .10 and .11 address sets explained, router and system setup, DoH and DoT, versus 1.1.1.1.
Performance
Forced Reflow: When Reading the DOM Costs You a Frame
Browsers batch layout work until something reads a geometry value. Do that inside a loop that writes, and one recalculation becomes one per iteration.
DNS
Ghost Domain: Why a Removed Delegation Still Resolves
A resolver learns your nameservers from two places, and the second one can refresh itself forever. That is why a nameserver migration can outlive its own TTL.