What counts as an entity
Mobs, players, items dropped on the ground, arrows, boats, minecarts, item frames, and armour stands are all entities. Each one is ticked, tracked, and sent to nearby clients.
The expensive ones are those that think: mobs with pathfinding and AI cost far more than a dropped item, and hundreds of them in one place create the classic farm-induced lag.
Mob caps and cramming
The mob cap limits how many hostile or passive mobs spawn per player in a loaded area. It is a spawning limit, not a hard cap on population: mobs that already exist keep living and ticking.
Entity cramming pushes entities apart when too many occupy a block. It prevents infinite stacking, but the pile still costs ticks — cramming manages behaviour, not performance.
Why piled-up entities lag servers
A mob farm with thousands of stored mobs forces the server to run AI, collision, and pathfinding for all of them continuously, whether or not anyone is watching. That is tick time stolen from everything else.
The same is true of a storage room with thousands of loose items, and of decorative builds using hundreds of item frames or armour stands.
Levers that exist
Vanilla offers few: keep populations down, use fewer decorative entities, and consider lowering max-entity-collisions if crammed mobs cause spikes. There are no per-chunk entity caps to tune.
Paper and Purpur expose entity activation ranges and explicit limits, which let distant mobs pause instead of ticking forever — the main reason a busy farm server runs a fork rather than vanilla.
FAQ
Common questions
Do dropped items cause lag?
Yes, and they are easy to overlook. Thousands of item entities tick, merge, and despawn on their own schedule, so cleaning up storage floors and farm overflow is one of the cheapest performance wins available.
Can I cap entities per chunk in vanilla?
No. Vanilla has mob caps for spawning and cramming for behaviour, but no per-chunk entity ceiling. Explicit entity and activation limits are a Paper feature, which is why lag-heavy servers move to it.
