Notes & guides
Diagnostic how-tos, HTTP reference, and notes on how isitdown.io probes the internet. Written for operators and curious users.
Java vs Bedrock: why you can't connect to a Minecraft server
Minecraft says the server is unreachable but your friend is on it right now? Java and Bedrock are two different games with different protocols, ports, and addresses — here's how to tell which side you're on.
MOTD, player count, ping: how Minecraft server status actually works
Where the server list gets its MOTD, player count, and latency from — the Server List Ping protocol, what it can and can't tell you, and why the player count is sometimes a lie.
CS2, Rust, ARK, Palworld: checking any Source-style game server
One query protocol covers a surprising number of games. How A2S works for CS2, TF2, Rust, ARK, and Palworld servers, why the query port isn't the game port, and where each game's quirks hide.
Why your Minecraft server dropped off server lists (and how to get back)
Server-list sites mark you offline or quietly delist you when their crawlers can't ping you. The usual causes — restart windows, DDoS filters, moved hosts, dead SRV records — and how to catch it before your traffic dies.
Server lists say your Minecraft server is offline, but you can join it fine
Your server accepts connections but every tracker shows it offline. That gap is the difference between a login handshake and a Server List Ping, and the fix depends on which one is failing.
Minecraft connection errors decoded: io.netty, timed out, refused, and the rest
What io.netty.channel.AbstractChannel$AnnotatedConnectException, Connection refused, Failed to login, and Timed out actually mean, and which of them are your problem to fix.
Server lag or server downtime? How to tell the difference before you restart
Players say the server is down. It's pinging fine. Lag and downtime look identical from the player's side and need opposite responses, here's how to separate them with evidence.
Give your Minecraft community a status page instead of a Discord ping
When your server goes down, everyone asks at once. A public status page answers before they ask, and gives you a record of what actually happened.
ERR_CONNECTION_REFUSED: what it means and how to fix it
ERR_CONNECTION_REFUSED means the server's IP actively rejected your connection. What sends a TCP reset, server vs client causes, and how to isolate it.
What does HTTP 500 Internal Server Error actually mean?
What a 500 Internal Server Error means, how it differs from 502, 503, and 504, the usual causes, and what users and site owners can each do about it.
What does HTTP 403 Forbidden actually mean? Blocked vs broken
HTTP 403 Forbidden means the server understood your request and refused it. How to tell an auth problem from a WAF or bot block, and what to do for each cause.
Cloudflare Error 521: Web Server Is Down, what it means and how to fix it
What Cloudflare error 521 means, how a refused connection differs from 520 and 522, the four origin misconfigurations behind it, and the owner fix checklist.
Is Roblox down? How to check if it's Roblox or just you
Roblox won't load or you can't join a game? How to tell whether Roblox itself is down or it's just you, and what errors 277, 279, 267 and 268 mean.
Is GitHub down? How to check Actions, the API, Pages, and git itself
GitHub's homepage can load while Actions, the API, or git push fails. How to check each GitHub component, read the official status feed, and triage fast.
Is Twitch down? Stream not loading vs a real platform outage
Twitch stream not loading? How to tell a platform outage from a player, chat, or login problem, plus what error 2000, 3000, and 4000 actually mean.
How to monitor your website's uptime for free (and what actually matters)
A practical guide to free uptime monitoring: what a good probe looks like, alert thresholds that avoid false alarms, email vs webhook alerts, and status badges.
Is Steam down? How to check the store, network, and game servers
Steam won't load, downloads stalled, or a game says 'servers unavailable'? How to tell whether Steam is down globally, one component is degraded, or it's your connection.
Is Coinbase down? Checking a crypto exchange during volatility
Coinbase frozen, trades failing, or the app spinning right when the market moves? How to tell whether Coinbase is down for everyone, throttling you, or it's your side, and why exchanges break under load.
SSO is down: how one identity-provider outage locks out everything
When your SSO or identity provider has an incident, every app behind 'Sign in with…' locks out at once. How to spot an IdP outage, why it cascades, and what you can actually do.
Is ChatGPT down? How to check OpenAI status in 30 seconds
ChatGPT stuck loading or the API throwing errors? How to tell in 30 seconds whether OpenAI is down for everyone, rate-limiting you specifically, or it's just your network.
Is Claude down? How to check Anthropic's status in under a minute
Claude not responding, or the Anthropic API erroring inside your app? How to tell fast whether Anthropic is down for everyone, throttling your key, or it's a problem on your side.
Is Gemini down? How to check Google's AI status
Gemini stuck, refusing to answer, or the API returning errors? A quick way to tell whether Google's AI is down globally, degraded, rate-limiting you, or it's a local problem.
Why your AI API keeps returning 429 (and how to stop it)
A 429 from OpenAI, Anthropic, or Google isn't an outage, it's a rate limit. What actually triggers RPM/TPM caps, how to back off correctly, and how to tell a limit apart from a real outage.
Is the AI API down, or just slow? How to tell them apart
Timeouts and long waits feel like an outage but usually aren't. How to distinguish a genuine LLM-provider outage from latency, throttling, or a long streaming response.
Is Discord down? How to check for everyone vs. just you
Discord won't connect, messages won't send, or voice keeps cutting out? A 60-second check to tell whether Discord is down globally, having a partial outage, or it's your network.
Is Cloudflare down today? How to read a Cloudflare outage
When Cloudflare has an incident, thousands of sites break at once. How to confirm it's really Cloudflare, which error codes point to it, and what you can (and can't) do about it.
Anatomy of a website outage: how sites actually go down
What happens between a working site and a 503 error, the failure categories, real named outages from each, and why status pages always lag the real impact.
HTTP 502 Bad Gateway: what it actually means and how to fix it
What 502 means, how it differs from 503 and 504, the half-dozen things that actually cause it, and how to diagnose one as either a user or an operator.
HTTP 504 Gateway Timeout: what causes it and how to fix it
504 vs 502 vs 408 vs Cloudflare 524, what each one means, what actually causes a 504 in production, and how to diagnose one fast.
DNS_PROBE_FINISHED_NXDOMAIN: what it means and 6 ways to fix it
What Chrome's NXDOMAIN error actually says, why it appears for sites that absolutely exist, and the diagnostic checklist that fixes it in under a minute.
SSL certificate expired: what it means and how to fix it
Why expired certs break sites in seconds, the calendar-driven outages this causes every year, and the operator + user playbook for fixing or working around one.
Cloudflare Error 520: 'Web Server Is Returning an Unknown Error'
What 520 actually says, the difference between 520 / 521 / 522 / 523 / 524, the 5 origin behaviors that cause it, and how to debug one with the cf-ray header.
Cloudflare Error 522: Connection Timed Out, what it means and how to fix it
Why 522 happens before any HTTP exchange, how it differs from 524 and 520, and the 6-step playbook for diagnosing one in under five minutes.
ERR_CONNECTION_TIMED_OUT: what it means and how to fix it
Why Chrome's connection-timeout error is usually a local problem, how to tell when it's the site instead, and the ordered checklist that fixes it fast.
Your Minecraft server says 0/0 players. Here's what's actually happening.
If your server pings as online but reports zero players when you know there are people on it, the cause is almost always one of four protocol-level quirks. Here's how to tell which.
How to check if a Minecraft server is online (without launching the game)
Hypixel, 2b2t, EarthMC, and the rest, a quick guide to telling whether a server is actually offline, just queueing you, or whether the problem is on your end.
A2S_INFO is the fastest smoke test for a Source-engine server
Before you SSH into the box, before you check the logs, fire one A2S_INFO packet. The response (or its absence) tells you which of five common failure modes you're looking at.
What runs on AWS? A field guide to the cascade
When AWS us-east-1 hiccups, dozens of unrelated consumer services go dark together. Here's the dependency map most people don't realize exists, plus how to read an outage when it actually happens.
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-method website checks: why a single request isn't enough
One request can't tell a real outage from a bot block or a protocol quirk. Here's what probing with 4 independent methods 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.