The graphs above the console are the fastest diagnostic you have. They are also easy to misread, because what looks alarming on a Minecraft server is often normal and what looks fine is sometimes the problem.
Memory: what each shape means
| Shape | Meaning |
|---|---|
| A sawtooth — climbs, drops, climbs | Normal. That is Java allocating and collecting. |
| Climbs and never drops | A leak, or genuinely too little memory for the workload. |
| Sits near the ceiling constantly | Under pressure. Expect freezes and eventually a crash. |
| Drops to near zero periodically | A restart. Check whether you scheduled it. |
CPU: what each shape means
| Shape | Meaning |
|---|---|
| Steady low with occasional spikes | Normal. Spikes are saves and chunk generation. |
| Pinned at roughly one core's worth | The main thread is saturated. This is what lag looks like. |
| High and rising with player count | Expected. Compare against TPS before worrying. |
| High with nobody online | Something is running on its own. Spawn chunks or a plugin. |
Minecraft's world simulation runs on one thread. One saturated core out of eight shows as roughly twelve percent, so a server can be completely maxed out while the graph looks relaxed. Read CPU alongside TPS, never on its own.
Using them to answer a question
- Look at the moment the complaint happened
«It lagged at nine» is answerable from the graph if you look at nine. Looking at now tells you about now.
- Compare the two lines
Memory at the ceiling with low CPU is garbage collection. High CPU with plenty of memory is work — a plugin, entities, or chunk generation.
- Then get TPS for the same moment
The graphs say what the machine was doing. TPS says whether the game was affected. You need both to know whether anything was actually wrong.
Knowing what your server's normal shape looks like on a good evening makes an abnormal one obvious at a glance. Without that baseline, every graph looks like it might be a problem.