How to Fix Mobs Not Spawning on a Minecraft Server

Direct answer

Check difficulty and the doMobSpawning gamerule, then determine whether the issue affects every world or just a farm. On Paper, inspect actual mob caps before raising limits.

What it means

Hostile natural spawning can be blocked by Peaceful difficulty, gamerules, caps, lighting, nearby players, despawn rules, world-specific settings or spawn-management plugins. Spawner cages and eggs are not the same spawning mechanism as natural mobs.

If you are a player

1. Ask whether mobs spawn elsewhere in the world at night. If so, investigate the farm’s biome, light, AFK position, available space and nearby caves rather than changing server-wide settings.
2. Check whether other players are using high-density mob farms in the same dimension. Multiplayer spawn distribution can differ from single-player.
3. Give the administrator the exact coordinates, dimension and expected mob type. Do not assume a non-spawning farm proves that all mobs are disabled.

If you run the server

1. Check the actual difficulty and natural-spawning gamerule from an authorized console. On Java 1.21.10 and earlier the gamerule was /gamerule doMobSpawning; in 1.21.11 and later it became /gamerule minecraft:spawn_mobs. Use the syntax for your installed version.
2. On Paper, compare /paper mobcaps and /paper playermobcaps <player>. A full cap calls for diagnosing existing population, not immediately increasing it.
3. Review server.properties, bukkit.yml and per-world config/paper-world-defaults.yml overrides for natural spawn limits and spawn intervals. Test defaults on a backup if an old optimization pack changed spawning.

References

• https://www.minecraft.net/en-us/article/minecraft-java-edition-1-21-11
• PaperMC commands
• PaperMC world configuration
• PaperMC troubleshooting

Related fixes and guides