NotTodayMob

Designed with simplicity and performance in mind, NotTodayMob provides configurable control over mob spawning without modifying world generation definitions or biome data. Individual mobs — or entire namespaces — can be blocked entirely, or have their natural spawn frequency increased or reduced using straightforward configuration.

NotTodayMob is intended for modpack creators and server administrators who want predictable, lightweight control over mob behaviour without complex datapacks or scripting.

All changes are applied at runtime and work automatically with modded mobs, modded biomes, and custom dimensions.

When unwanted mobs try to spawn, the answer is simple: not today.

Latest Update - Version 1.0.6

NotTodayMob now includes expanded control over natural and custom mob spawning.

The naturalSpawnWeightMultipliers setting allows pack creators and server administrators to reduce, increase, or disable natural spawning for matching entities.

A new customSpawnChanceMultipliers setting also allows spawn attempts using the EVENT or TRIGGERED spawn types to be reduced or disabled independently, providing support for mods that use custom event-based spawning.

Features

Block specific mob spawning
Adjust natural spawn frequency using configurable weight multipliers
Optionally replace/remove matching spawners during chunk loading
Automatically removes spawn eggs and spawners from player inventories/in world
Additional fine-grained control for baby variants with support for vanilla and modded mobs that expose baby/adult state through standard Minecraft entity behaviour
Supports exact IDs and wildcard matching including dimension-specific rule scoping
Periodic performance statistics logging
Works automatically with modded mobs and biomes
No biome or world generation changes required
Lightweight and safe for large modpacks
Server and multiplayer friendly

Note

On Forge 1.20.1 and NeoForge 1.21.1, matching spawners are first replaced with an inert spawner before being safely removed on a later chunk load.

This staged removal avoids chunk-loading warnings caused by removing block entities too early during world generation.

Typical Use Cases

Reduce the number of specific mobs in survival gameplay
Increase the presence of certain creatures in themed worlds
Disable problematic or unwanted modded mobs
Balance mob populations in large modpacks
Fine-tune difficulty without editing datapacks

Configuration Guide

NotTodayMob is configured using a small set of server-side settings designed to be predictable and easy to understand. Changes can be made at any time and will apply automatically after restart or reload.

Core Behaviour

blockEntitiesEnabled

Controls whether matching entities are prevented from spawning.

Default: true

If disabled, all entity blocking rules are ignored.

blockBabyVariants

Controls whether baby variants of blocked entities are also blocked.

Default: true

If disabled, baby variants will still spawn even when the adult equivalents are blocked.

World-Generated Spawner Handling

worldgenSpawnerRemoval

Controls whether matching world-generated spawners are removed or replaced during chunk loading.

Default: true

If enabled, matching spawners will be:

Replaced using worldgenSpawnerReplacements, or
Removed if no valid replacement is defined

If disabled, world-generated spawners remain unchanged.

worldgenSpawnerReplacements

worldgenSpawnerReplacements = [
    "minecraft:zombie"
]

Behaviour

Applies only to world-generated spawners (e.g. dungeons, structures)
Only accepts exact entity IDs
Replacement occurs automatically when a chunk is generated or loaded
Multiple entries can be provided as fallbacks
If no valid replacement is defined, the spawner is removed instead
Existing worlds will be updated as chunks are loaded

Example

blockedEntities = [
    "minecraft:skeleton",
    "minecraft:*spider"
]

worldgenSpawnerReplacements = [
    "minecraft:zombie"
]

Here, skeleton or spider spawners found during chunk loading will become zombie spawners

Spawner and Spawn Egg Controls

suppressBlockedEntitySpawners

Controls whether matching spawners are blocked from use.

Default: true

If disabled:

Spawners remain usable
Entity spawning behaviour still follows blocking rules

suppressBlockedEntitySpawnEggs

Controls whether matching spawn eggs are blocked from use.

Default: true

If disabled:

Spawn eggs can still be used
Entity spawning behaviour still follows blocking rules

Inventory and Item Cleanup

cleanupDroppedItems

Controls whether spawn eggs and spawners for blocked entities are removed immediately when dropped into the world.

Default: true

Disable this if you want blocked items to exist but still prevent spawning.

inventoryCleanupIntervalTicks

Controls how often (in ticks) player inventories are checked for blocked spawn eggs and spawners.

Default: 10

Ticks	Actual Time
`10`	Half a second
`20`	One second

Higher values reduce overhead but delay cleanup.

enableStatsLogging

Controls whether periodic NotTodayMob summary statistics are written to the server log.

Default: false

statsLoggingIntervalTicks

Controls how often (in ticks) summary statistics are logged.

Default: 12000

Ticks	Actual Time
`12000`	Ten minutes
`24000`	Twenty minutes

statsLoggingVerbose

Controls whether additional detail is included in each statistics report.

Default: false

When enabled, reports may include:

Top blocked entities
Rule match breakdowns

statsLoggingToSeparateFile

Controls whether statistics are also written to a dedicated log file.

Default: false

When enabled, statistics will also be written to logs/nottodaymob.log

Blocking Entities

blockedEntities

Defines which entities are prevented from spawning.

Supports:

Exact IDs
Namespace wildcards
Prefix and suffix wildcards
Optional dimension scoping

Examples

blockedEntities = [
    "minecraft:skeleton",
    "minecraft:*spider",
    "alexsmobs:*",
    "minecraft:zombie|dimensions=minecraft:overworld"
]

blockedBabyEntities

Defines which baby variants are prevented from spawning without blocking their adult counterparts.

Supports:

Exact IDs - Namespace wildcards
Prefix and suffix wildcards
Optional dimension scoping

Examples

blockedBabyEntities = [
    "minecraft:zombie", 
    "minecraft:*piglin", 
    "alexsmobs:*", 
    "minecraft:hoglin|dimensions=minecraft:the_nether"
]

Scope Rules to Specific Dimensions

Rules can optionally be limited to one or more dimensions using inline dimensions= filtering.

blockedEntities = [
    "minecraft:skeleton|dimensions=minecraft:overworld",
    "minecraft:blaze|dimensions=minecraft:the_nether",
    "alexsmobs:*|dimensions=twilightforest:twilight_forest"
]

Behaviour

Limits the rule to the specified dimension(s)
Multiple dimensions can be provided using commas
If no dimensions= filter is present, the rule applies to all dimensions
Works with both vanilla and modded dimensions
Supports exact IDs and wildcard matching

Example

blockedEntities = [
    "minecraft:zombie|dimensions=minecraft:overworld"
]

Here, zombies are blocked only in the Overworld, while remaining unaffected in other dimensions.

Adjusting Natural/Custom Spawn Frequency

naturalSpawnWeightMultipliers

Adjusts natural spawn frequency for matching entities.

naturalSpawnWeightMultipliers = [
    "minecraft:zombie=0.5",
    "minecraft:creeper=2.5",
    "minecraft:bat=0.0"
]

Format: entity_or_pattern = multiplier

Multiplier Behaviour

Multiplier	Effect
`0.0`	Disables natural spawning
`0.5`	Half as common
`1.0`	Vanilla behaviour
`2.5`	Roughly 250% spawn frequency
`10.0`	Maximum supported multiplier

Weight adjustments apply only to natural spawning. Spawner, command, and other spawn sources are unaffected.

customSpawnChanceMultipliers

Adjusts spawn success chance for matching entities created through EVENT or TRIGGERED spawn types.

customSpawnChanceMultipliers = [
    "simpleenemymod:ruunit=0.1",
    "simpleenemymod:usunit=0.1",
    "examplemod:boss=0.0"
]

Format: entity_or_pattern = multiplier

Multiplier Behaviour

Multiplier	Effect
`0.0`	Disables matching custom spawns
`0.1`	Allows roughly 10% of attempts
`0.5`	Allows roughly half of attempts
`1.0`	Original spawning behaviour

Chance adjustments apply only to EVENT and TRIGGERED spawns. Natural, spawner, spawn egg, command, and other spawn sources are unaffected.

Compatibility

NotTodayMob works automatically with:

Modded mobs and biomes
Custom dimensions
Datapack-driven spawning

No special integration is required.

Reporting Issues

If you encounter a compatibility issue with another mod, please report it via the project issue tracker so it can be investigated.