Notes & guides
Diagnostic how-tos, HTTP reference, and notes on how isitdown.io probes the internet. Written for operators and curious users.
Is it down for everyone or just me? How to tell in 60 seconds
A three-step diagnostic that tells you whether a site outage is global, regional, or just your own network — before you escalate anything.
What does HTTP 503 Service Unavailable actually mean?
The difference between 503 and 500, 502, 504 — what each code means, what causes 503 specifically, and how to diagnose one in under a minute.
Multi-region website checks: why a single ping isn't enough
A single-region ping can't tell a global outage from a regional one. Here's what probing from 4 regions in parallel reveals — with real examples.
Cloudflare Error 1020 Access Denied: what it means and how to fix it
Error 1020 is a deliberate block by the site owner's Cloudflare firewall, not an outage. Here's how to diagnose why you're blocked and what to do next.
DNS propagation: why it really takes hours (and when it doesn't)
DNS doesn't actually propagate — resolvers cache records until their TTL expires. Here's what controls the real wait time and how to speed it up.
Flush DNS cache: exact commands for Windows, macOS, Linux, and Chrome
The right command for every OS, when to use it, and how to verify the cache actually cleared. Plus what flushing won't fix.
HTTP 429 Too Many Requests: what triggers it and how to handle it
What 429 means, how it differs from 503 and 1015, when servers send it, and the right way to back off without making the problem worse.
Cloudflare Error 1015: what "You are being rate limited" actually means
1015 is a Cloudflare-edge rate limit, not an outage. Here's why it triggers, how it differs from 1020 and 429, and what to do as a user or site owner.