What entities cost
Every mob, dropped item, arrow, minecart and armour stand is an entity that gets ticked 20 times a second. Ten thousand of them and the tick budget is gone. Farms produce entities in bulk: a mob farm 200 zombies, an iron farm dozens of golems, an item farm with a broken hopper line thousands of items on the floor.
Find the culprit
/paper entity list(Paper) shows counts by type and which chunk holds the most. Teleport there.spark tickmonitoror a Spark report shows the area.
Cap it
bukkit.yml → spawn-limitscaps natural spawns per player.paper-world-defaults.yml → entities.spawning.per-player-mob-spawns: truestops one player's farm from eating everyone's mob cap.- Item despawn: items disappear after 5 minutes by default;
spigot.yml → item-despawn-rate(in ticks) lowers it. - Merge radius (
spigot.yml → merge-radius) stacks nearby items and XP into one entity. - Plugins like EntityClearer or ClearLag remove excess entities on a timer with a warning.
Chunk loaders
A chunk stays loaded only while a player is nearby, unless something forces it: spawn chunks, portals, or a mod's chunk loader. Forced-loaded chunks tick forever, farms in them run 24/7. On a vanilla/Paper server: /forceload query lists them; keep them few. On modded servers, limit chunk loaders per player with the mod's config.
Rules that work
Whitelist the number of loaded chunks per player, cap farm output with a maximum entity count per chunk, and say it in your rules. Most players build responsibly once they know what a lag machine is.