Live network outages, your own connection, and your group. Drag to move, scroll to zoom.
Anything you set here is a claim, not a measurement. Your code will say so, and whoever pastes it will see that.
A browser can time HTTP requests but can't measure UDP packet loss the way a game engine does. Treat all of this as a strong indicator, not a netgraph.
Add the people you play with. You will see whose internet is affected, and who should host.
They open lagcheck.com on their own device and run the check. It gives them a code to send you — nothing is collected about them, and nothing leaves their browser unless they choose to paste it.
Enough to tell you whether their provider is down or their region is affected — but they can't be ranked as a host until they run a check.
Most lag has one of two causes, and they need opposite fixes. Either something on the way out of your house is delaying your traffic, or the service you are trying to reach is having a bad day. A speed test answers neither question: a gigabit line can feel unplayable, and a service can be down while your connection is flawless. lagcheck measures your own line and reads the game's own status feed at the same time, then tells you which side the problem is on.
Idle latency — your round trip to the nearest edge with nothing else running. Mostly a fact about geography.
Latency under load — the same round trip measured while your upload is saturated. This is bufferbloat, and it is the usual reason a fast connection still feels terrible: your router queues packets behind a big transfer and everything you send waits its turn. A line that idles at 20 ms and goes to 400 ms under load will lose you fights, and a speed test will call it excellent.
Jitter — how much the round trip swings between samples. Games predict where you will be; jitter breaks the prediction, which is why a high-jitter line feels worse than a slower steady one.
Upload — graded against what you are actually trying to do, using the same per-player budget the host picker uses. Not against a generic scale, because how much upload is "enough" depends entirely on the game and the size of the group.
Those four roll into one score out of 100 and a letter. The letter is a band of the score rather than a separate opinion about it, and the score can never come out better than the worst of the three latency measurements — one catastrophic number cannot be averaged away by two good ones.
The result is laid out as a path: you to your router, your line to the edge, the edge to the game, and inside the game itself. Each segment says how we know — measured here, reported by the vendor, or not visible at all. A browser cannot see inside your house, so that first segment stays grey rather than being quietly coloured in.
Your network is matched against a live feed of networks currently in outage worldwide, by the number that identifies your provider. If your ISP is the one on fire, you will be told, and no amount of restarting your router will help.
For a peer-hosted session the right host is not whoever pays for the fastest plan. It is whoever's worst connection to anyone else in the group is least bad — geography and upload decide that, not advertised speed. Everyone runs the check, shares a short code, and the group is ranked. The codes are pasted by hand on purpose: nothing about anyone is uploaded, and there is no account and no group stored on a server.
The check measures to a nearby edge, not to the specific server hosting your match, and it times HTTP requests rather than the UDP traffic a game actually sends — so it cannot report packet loss. Both limits are stated here rather than papered over. More about how this works, or read the privacy page.