Just Another Spawner Mod Wiki

Just Another Spawner (JAS) is a Minecraft Mod aimed at providing an alternative entity spawning system that offers greater control, flexibility, and possibilities than the vanilla system. It runs in parallel with the vanilla system, meaning it can either replace vanilla spawning entirely or work alongside it.

By default, JAS imports settings from all declared entities in Minecraft, including those added by other mods (such as Mo' Creatures, Lycanites Mobs, or Project Zulu). It then allows users to manipulate nearly every property involved in the spawning process, from biome-specific weights to complex environmental logic using a custom tag system.

JAS functions by assigning a LivingHandler to every entity type. This handler determines the creature's category, whether it should use default mod location checks, and if it should be forced to despawn.

Parallel Spawning

JAS does not technically "remove" the vanilla spawner; instead, it disables it by emptying the vanilla biome spawn lists. This allows JAS to take full control of the spawning cycle. Because it is independent, it can handle mob caps and spawn rates more efficiently than the default system, preventing "spawn-gasms" where hundreds of mobs appear at once.

The Spawning Cycle

1. Import: On first run, JAS scans all loaded mods for entities.
2. Categorization: Entities are assigned to categories (MONSTER, CREATURE, etc.).
3. Location Check: JAS checks the SpawnListEntries to see if the entity is allowed in the current biome.
4. Logic Evaluation: JAS evaluates any Tags (e.g., light levels, block types) assigned to the entity.
5. Execution: If all conditions are met, the entity is spawned.

The mod's configuration is highly modular, located in the config/JustAnotherSpawner/ directory. It is divided into a Master directory (templates) and WorldSettings (world-specific overrides).

The heart of JAS is its tag system, which allows for complex boolean and numeric logic. Tags are used in the Spawn Tag and Despawn Tag fields of the configuration files.

Boolean Tags

These tags return true or false to allow or block a spawn.

• spawn: The primary tag for allowing a spawn.
• despawn: Controls if an entity should be removed when far from players.
• !: The NOT operator (e.g., !solidside means the block must not have a solid side).

Property Tags (v0.14.0+)

These tags check environmental variables at the spawn location.

Entities are grouped into categories that share a common spawn cap and tick rate. By default, JAS creates the following:

• MONSTER: Hostile mobs that spawn in the dark (Cap: 70).
• CREATURE: Passive animals like cows and sheep (Cap: 10).
• AMBIENT: Small decorative mobs like bats (Cap: 15).
• WATERCREATURE: Aquatic mobs like squid (Cap: 5).
• NONE: Entities in this category are ignored by the JAS spawner.

Users can create custom categories in CreatureType.cfg to separate specific mod mobs (e.g., a BOSS category with a cap of 1).

JAS provides native support for vanilla and modded structures. This allows you to define unique spawns that only occur within the bounding box of a structure, regardless of the biome.

Supported vanilla structures include:

• WitchHut: Spawns Witches.
• NetherBridge: Spawns Blazes, Wither Skeletons, and Magma Cubes.
• Mineshaft: Can be configured for Cave Spiders.
• Stronghold: Can be configured for Silverfish or custom guards.

Structure spawns are defined in StructureSpawns.cfg using the format S:StructureName=EntityName-Weight-MinPack-MaxPack.

JAS includes several administrative commands to help debug and manage spawns in real-time.