Mods Program

Mob Spawn Checker (MSC)

• 9/7/26 2:26 am
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  • save_alt 7 downloads
Game Version
Minecraft 1.20.1
Progress
100% complete
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JoaoCruz
Lvl 8 • Apprentice Explorer
2
Mob Spawn Checker (MSC) Minecraft Mod

Mob Spawn Checker (MSC) is the ultimate diagnostic tool designed for mod developers and modpack creators to save hours of tedious testing. Tired of wandering around your world trying to figure out if your newly added custom mobs are actually spawning? With MSC, you can test and inspect mob spawn mechanics in real-time.

Simply press K to open the mob catalog, select any mob, and run a spawn test. The mod monitors the environment for 5 seconds (for monsters) or 20 seconds (for creatures) and breaks down exactly why a mob is or isn't spawning, highlighting the exact failure step if it gets blocked.

Mob Spawn Checker (MSC) Minecraft Mod

Key Features:
  • Real-Time Spawn Testing & Diagnostics:
  • Runs active tests to determine if a mob attempts and succeeds in spawning, utilizing an 8-door verification pipeline (Game Rules, Difficulty, Biome/Dimension, Mob Cap, Floor/Terrain, Light Level, Free Space, and World Insertion).
  • Comprehensive Catalog & Filters: Search for mobs by their English names regardless of language, filter by favorites, view mobs without spawn eggs, or isolate mod-specific mobs.
  • Environment Controls: Quickly toggle between Day, Night, Weather conditions, and teleport to valid biomes or dimensions right from the interface.
  • Variant & Custom Support: Switch between mob variants and manually spawn entities in Creative mode. Compatibility for external modded mobs.
  • Multi-Language Support: Fully translated into English, Portuguese (BR), German, Spanish (ES), French, Russian, Turkish, and partially Simplified Chinese.

Mob Spawn Checker (MSC) Minecraft Mod

1 Update Logs

1.0.0 : by JoaoCruz 09/07/2026 2:28:21 amSeptember 7 @ 6:28 am UTC

UPDATE 1.0.0

[NEWS]

  • Official release of MobSpawnChecker (MSC), now you can check if your modded or vanilla mobs are spawning correctly.

[FEATURES]
  • To open the mob screen, press K.
  • To save favorite mobs, click the heart on the right side of the mob.
  • To enable mobs without spawn eggs, enable the option in the top field next to the favorites tab.
  • Configuration screen to mute the sliding sound between eggs.
  • You can search for the original English name while using any language.
  • You can select to show only modded mobs.
  • You can toggle the view between variants of the same mod. (Vanilla and Cannibal Villages mobs work perfectly, but since each mod has its own variant method, it may not work perfectly with all of them).
  • You can spawn the mob manually (in Creative mode).
  • You can change to Day, Night, Weather conditions, and biome teleportation directly in the catalog screen.
  • You can filter the biome/dimension you want to teleport to, including favoriting biomes.
  • By clicking on the mob, you can view its spawn conditions.
  • You can increase the amount of "creature" mobs generated per chunk to test more easily.


[SPAWN TEST]
  • When clicking to run a test, it will run for at least 5s for monsters and 20s for creatures. By clicking K again, the test ends and shows whether the mob is spawning, and if not, at which stage it was blocked.
  • You can check the result of the last test by clicking the back button on the mod's home screen (K) next to the settings icon.
  • To end the test before the minimum time, double-click K (ending the test before the recommended minimum time greatly increases the chance of false positives/negatives).


[OTHERS]

  • The mod was designed primarily to be compatible with modded mobs; however, since each modder/mod codes their mob in a specific way, even applying various filters, MSC may not be able to detect all mobs with 100% accuracy. (Except Vanilla and Cannibal Villages, due to sharing the same author as MSC).

  • Language support: English, Portuguese (BR), German, Spanish (ES), French, Russian, Turkish, and Chinese (Simplified) (partially).

[SUCCESS RATE]

  • The mod has a 94% to 96% accuracy in data reading efficiency, reserving the rest for false positives/negatives caused by occurrences not covered by the code.

  • Version 1.0.0 False Negative Rate: 4% to 7%.

  • Door-by-Door Accuracy:

    • 1. Spawn Rule (100%): Reads the server's GameRules.RULE_DOMOBSPAWNING directly.

    • 2. Difficulty (100%): Checks the official Difficulty enum and mob category.

    • 3. Biome and Dimension (95%): Scans the world's biome registry, structures, and Biome Modifiers.

    • 4. Mob Cap (98%): Reads the SpawnState memory and performs an entity-by-entity census in loaded chunks.

    • 5. Floor and Terrain (92%): The Mixin intercepts isSpawnPositionOk and the heightmap ignores trees to find actual grass.

    • 6. Light Level (94%): Intercepts the mob's internal rules and offsets real night sky darkness.

    • 7. Free Space (96%): Directly intercepts the hitbox collision check (checkSpawnObstruction).

    • 8. World Insertion (99%): Registers via unique UUID on the server thread without duplicate counting.

  • Note: If an external mod creates a mob that ignores the biome table and only spawns via its own event script at its mod's tick rate, Door 3 may flag a lack of natural biome because it doesn't use the standard Minecraft system.

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