Spawn Detective

v0.1.0-alpha.1

First release. Alpha because it has never been run outside a development environment, not because anything is known to be broken.

Minecraft 1.21.1 / NeoForge 21.1.230. Same mod as the 26.1 line, same answers, built against this version's spawn code. Take the jar whose name carries your game version.

What it does. Anchor a block with the Spawn Probe, walk away, pick a mob, and it tells you whether that mob can spawn there and which rule stopped it. It walks Minecraft's real spawn pipeline rather than reimplementing it, so it answers for mobs from any mod, including ones it has never heard of.

• Spawn Probe. Sneak-right-click a block to anchor it, walk 25 blocks away, right-click to read. The two steps exist because standing next to a block breaks two real spawn rules: nothing spawns within 24 blocks of a player, and your own body fills the space a mob needs. Crafted from a sapling over a stick.
• Report screen. One mob, one answer. Search any mob by name or id, or pick from the ones the biome actually spawns there. The choice sticks between blocks and survives a relog. Below the verdict, the mob's full walk through every gate with the measurement behind each one.
• Green, red, yellow. Green spawns. Red never will. Yellow means only something temporary is stopping it, like a full mob cap - it will spawn once that clears. Those need different actions, so they are different colours.
• Jade support. Hold the probe with a mob selected and the look-at tooltip shows that mob's verdict for the block you are looking at, live. Colours are inverted there: when you are spawn-proofing, a possible spawn is the bad news.
• JEI support. An info page on the probe explaining the gesture.
• /spawndetective for the console and command blocks, including /spawndetective for <entity> to ask about one mob and a whole-position sweep.
• Config. crafting.enabled turns the recipe off for packs that would rather hand the item out themselves.

Known limits, stated rather than hidden.

• Where a cause cannot be narrowed down, the report says so and offers leads instead of picking one. A vague true answer beats a precise false one.
• Beyond the floor, it cannot yet name which mob-specific condition is failing - the ones a monster spawner would bypass, like a drowned needing water.
• It reports that another mod vetoed a spawn, but not which mod.
• English only.
• The item texture is placeholder art.