Spawn Mobs Active

Spawn Mobs Active is a lightweight, fully configurable mob-spawning manager for Fabric 1.21.1. With a simple rule list you decide exactly which mobs may spawn and which are blocked — by mob, category, spawn source, dimension, height, light level, and biome. No commands or coding required: everything lives in one easy JSON file.

Whether you want a peaceful overworld where monsters only come from spawners, a cave-only zombie experience, or just to get rid of one annoying mob — Spawn Control makes it a couple of lines.

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Features

• Block or allow any mob individually (minecraft:creeper, minecraft:zombie, …)
• Block or allow whole groups via category (e.g. all MONSTERs at once — works for modded mobs too)
• Filter by spawn source: natural, spawner, structure, patrol, and more
• Filter by dimension (Overworld / Nether / End / modded dimensions)
• Filter by height (minY / maxY) — great for "caves only"
• Filter by light level and sky visibility (surface vs. cave)
• Filter by biome
• Dedicated options to handle chicken jockeys
• In-game reload — no restart needed
• Optional logging that prints every blocked spawn with its exact mob ID

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How it works (the important part)

You write a list of rules. Each rule is either ALLOW (let it spawn) or DENY (block it).

When a mob tries to spawn, Spawn Control checks the rules top to bottom and applies the first rule that matches — then it stops. If no rule matches, the defaultAction is used (normally ALLOW, i.e. vanilla behaviour).

The first matching rule wins. That's why "exceptions" (ALLOW) always go above the general ban (DENY).

A rule is just conditions (what must be true) plus one action. Any field you leave out is ignored, meaning "applies to everything." Within a single rule, all listed conditions must match (AND).

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Config file

Location: config/spawncontrol.json (created automatically on first launch, with examples).

Top-level settings

Setting	Meaning
enabled	Master switch for the whole mod (true / false)
defaultAction	What happens when no rule matches: "ALLOW" (vanilla) or "DENY"
disableChickenJockeys	true = no chicken is created as a mount; the baby mob stays on the ground
removeChickenJockeyRiders	true = removes the entire chicken jockey (rider and chicken), from any spawn source
logBlockedSpawns	true = print every blocked spawn + its mob ID to the console (great for finding IDs)
rules	The list of rules, checked top to bottom

Rule fields

Field	Meaning
action	"ALLOW" or "DENY"
entities	List of mob IDs, e.g. ["minecraft:zombie", "minecraft:creeper"]. Empty = all
categories	Mob categories (see below). Empty = all
spawnReasons	Spawn sources (see below). Empty = all
dimensions	e.g. ["minecraft:overworld", "minecraft:the_nether"]. Empty = all
biomes	e.g. ["minecraft:plains"]. Empty = all
minY / maxY	Height range (inclusive)
requireSkyVisible	true = surface only, false = caves only
minBlockLight / maxBlockLight	Block-light range (0–15)
minSkyLight / maxSkyLight	Sky-light range (0–15)
comment	Free text note for yourself; has no effect

Categories

MONSTER, CREATURE, AMBIENT, WATER_CREATURE, WATER_AMBIENT, UNDERGROUND_WATER_CREATURE, AXOLOTLS, MISC

MONSTER covers hostile mobs (zombies, skeletons, creepers, spiders, endermen, witches, pillagers, …) — including modded mobs registered in that category.

Spawn reasons

NATURAL, SPAWNER, STRUCTURE, CHUNK_GENERATION, PATROL, JOCKEY, REINFORCEMENT, and others.

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Examples ("recipes")

Disable one mob completely (any source):

{ "action": "DENY", "entities": ["minecraft:creeper"] }

Disable all hostile monsters everywhere:

{ "action": "DENY", "categories": ["MONSTER"] }

Monsters only from spawners (allow spawners, block the rest):

{ "action": "ALLOW", "categories": ["MONSTER"], "spawnReasons": ["SPAWNER"] },
{ "action": "DENY",  "categories": ["MONSTER"] }

Only block monsters in the Overworld (Nether and End stay normal):

{ "action": "DENY", "categories": ["MONSTER"], "dimensions": ["minecraft:overworld"] }

Zombies only in caves (below Y 50), not on the surface:

{ "action": "ALLOW", "entities": ["minecraft:zombie"], "spawnReasons": ["NATURAL"], "dimensions": ["minecraft:overworld"], "maxY": 50 },
{ "action": "DENY",  "entities": ["minecraft:zombie"], "spawnReasons": ["NATURAL"], "dimensions": ["minecraft:overworld"] }

Tip: Build rules by asking first "what should be allowed as an exception?" → put that as ALLOW near the top, then put the general DENY below it.

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Chicken jockeys

Chicken jockeys are created in a special way and don't go through the normal spawn check, so they have their own settings:

• removeChickenJockeyRiders: true → removes the whole jockey (the riding baby mob and its chicken), no matter the spawn source. Already-saved jockeys are also cleaned up on load. Normal zombies and normal baby zombies are untouched.
• disableChickenJockeys: true → only prevents the chicken mount from being created; a normal baby mob remains on the ground.
• Per-rule alternative (removes just the chicken): { "action": "DENY", "entities": ["minecraft:chicken"], "spawnReasons": ["JOCKEY"] }

Both switches default to false.

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Commands

Requires OP / permission level 2:

• /spawncontrol reload — reload the config without restarting
• /spawncontrol on / /spawncontrol off — toggle the mod globally
• /spawncontrol status — show current status and rule count

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Good to know

• Trial spawners (from Trial Chambers) use their own logic and are not affected by this mod.
• Spawn Control only prevents new spawns; mobs already loaded in the world are not removed (let them despawn or clear them yourself).
• Tweaked something? Run /spawncontrol reload and you're set.

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Requirements

• Minecraft 1.21.1 (Fabric)
• Fabric API
• Java 21