Spawning Overhaul

A Minecraft mod that creates a more immersive mob spawning system based on environmental factors like caves, forests, and structures.

Features

Environment-Based Spawning

Instead of mobs spawning uniformly everywhere, this mod makes spawning rates dependent on the spawn location's environment:

Base Multiplier: Configure a global spawn rate that applies everywhere (default: 0.2x)
Cave Spawning: Progressive scaling based on depth
- Shallow caves (Y=60): Minimum multiplier (default: 1.0x = 20% acceptance)
- Deep caves (Y=-64): Maximum multiplier (default: 5.0x = 100% acceptance)
- The deeper you go, the more dangerous it gets!
Forest Spawning: Progressive scaling based on tree density
- Sparse areas: Minimum multiplier (default: 1.0x)
- Dense forests/jungles: Maximum multiplier (default: 3.0x)
- More trees = more danger
Structure Spawning: Dangerous structures have increased spawn rates (default: 3.0x)
- Strongholds, Nether Fortresses, Ocean Monuments, Woodland Mansions, Mineshafts, Dungeons

Note: Spawn multipliers use normalized probability acceptance based on the highest configured multiplier. With default settings (maxCaveMultiplier = 5.0), the reference is 5.0x:

0.2x base = 4% acceptance (0.2/5.0)
1.0x shallow caves = 20% acceptance (1.0/5.0)
5.0x deep caves = 100% acceptance (5.0/5.0)

This creates dramatic contrast: deep caves have 25x more spawns than the surface!

Mob-Specific Rules

Configure special spawn restrictions for specific mobs:

Spider Only In Cave (Enabled by default)
- When enabled: Spiders and cave spiders only spawn in caves
- When disabled: Spiders spawn normally everywhere
Disable Creeper Near Structure (Disabled by default)
- When enabled: Prevents creepers from spawning in dangerous structures (protects against griefing)
- When disabled: Creepers spawn normally in structures

In-Game Debug Command

Use /spawndebug to see what spawn rates would apply at your current position:

Environment detection at your position (cave, forest density, structure)
Active spawn multipliers and their ranges
Which multiplier would be used (base, cave, or forest)
Final calculated spawn rate if a mob were to spawn here

This shows you what the spawn system "sees" at your position.

Requires operator level 2 (use /op <username>)

Configuration

The mod creates a config file at config/spawningoverhaul.json5

Accessing the Config GUI

Fabric:

Install Mod Menu
Click "Mods" in the main menu
Find "Spawning Overhaul" and click the config button

NeoForge:

Click "Mods" in the main menu
Find "Spawning Overhaul" and click "Config"

Configuration Options

Environmental Multipliers

Option	Default	Description
Enable Immersive Spawning	✅ Enabled	Master toggle for the entire system
Base Multiplier	1.0x	Global spawn rate applied everywhere
Min Cave Multiplier	1.0x	Spawn rate at shallowest cave depth (Y=60)
Max Cave Multiplier	5.0x	Spawn rate at deepest depth (Y=-64)
Min Forest Multiplier	1.0x	Spawn rate in sparse areas
Max Forest Multiplier	3.0x	Spawn rate in dense forests
Dangerous Structure Multiplier	3.0x	Additional multiplier in dangerous structures
Enable Structure Modifications	✅ Enabled	Apply structure-based spawn changes

Mob-Specific Rules

Option	Default	Description
Spider Only In Cave	✅ Enabled	Restricts spiders to caves only
Disable Creeper Near Structure	❌ Disabled	Prevents creepers in structures (anti-griefing)

Detection Settings

Option	Default	Description
Dense Forest Log Threshold	50	Number of logs needed to count as dense forest
Dense Forest Scan Radius	10	Radius in blocks to scan for logs

Mod Compatibility

Option	Default	Description
Additional Dangerous Structures	`[]`	List of modded structure IDs to treat as dangerous
Additional Safe Structures	`[]`	List of modded structure IDs to treat as safe

How It Works

Spawn Calculation

For each mob spawn attempt, the mod:

Detects the environment at the spawn location (not the player's location):
- Is the spawn position in a cave? What's the depth?
- How dense is the forest at that position? (counts nearby log blocks)
- Is the spawn position in a dangerous structure?
Calculates multipliers:
- Starts with the base multiplier
- Calculates cave multiplier (if in cave)
- Calculates forest multiplier (if logs detected)
- Selects the highest of: base, cave, or forest
Applies additional modifiers:
- Multiplies by structure multiplier (if in dangerous structure)
- Applies mob-specific rules (spiders, creepers)
Makes the spawn decision:
- All multipliers use probabilistic acceptance normalized to the highest configured multiplier
- The reference maximum is dynamically calculated from config (max of cave/forest/structure multipliers)
- Higher multipliers = higher acceptance probability = more spawns
- Examples (with default 5.0x reference from maxCaveMultiplier):
  - 0.2x → 4% acceptance (very few spawns)
  - 1.0x → 20% acceptance (reduced spawns)
  - 3.0x → 60% acceptance (structures, many spawns)
  - 5.0x → 100% acceptance (deep caves, maximum spawns)
- Multiplier = 0.0: Always denies spawn

Performance

The mod is designed to be lightweight:

Cave detection: Simple Y-coordinate check + sky visibility
Forest detection: Cylindrical scan limited to ±3 blocks vertically
Structure detection: Cached with 10-second TTL
Target impact: <2ms per spawn check on average

Compatibility

✅ Compatible With

Modded mobs: Automatically works with any mob from any mod
Modded structures: Use config lists to mark modded structures as dangerous/safe
Modded biomes: Works in all biomes (vanilla and modded)
Other spawn mods: Applies after vanilla spawn checks, stacks with other mods

⚠️ Known Limitations

Does not affect mob spawners (only natural spawns)
Does not affect event spawns (raids, boss fights, etc.)
Does not affect command summons (/summon)
First spawn in each chunk may be slightly slower due to cache misses