What BiomeSpy does
BiomeSpy, made by MoePus, changes how Minecraft searches for biomes. It goes after two things: the /locate command and the Nature Compass. Both can take a long while to finish a scan, and the project says the wait can even crash a server. BiomeSpy replaces the search algorithm behind them so the lookups finish sooner.
On Modrinth it's filed under Miscellaneous.
The speed numbers
The project says biome locate time drops by up to 97%. For structure locate it says up to 90%. Read the "up to" literally. Those are the author's best-case figures, not a promise for every world or every search. The project page doesn't describe a benchmark setup, so don't expect the same result everywhere.
How it gets there
The mod assumes that five of the noise functions used during world generation don't depend on height. That assumption is what lets it skip a large amount of search work. According to the project, accuracy isn't affected, and cave biomes can still be found.
Worldgen and config
BiomeSpy makes no worldgen changes. It also needs no config. There's nothing to tune, which keeps things simple for anyone who just wants faster searches.
Modded biomes
The project lists support for TerraBlender and AlexsCaves biomes. It also says the mod was tested and verified on All The Mods 10. That's the only modpack named, so don't read it as a guarantee for other packs.
Who it suits
It fits server owners who watch /locate hang or crash their server. The result also fits modpack builders who use TerraBlender or AlexsCaves and want those biomes searched faster. If you never run /locate or use the Nature Compass, there's little here for you.
Compatibility
BiomeSpy supports Neoforge, Fabric and Forge. The Minecraft versions listed are 26.1.2, 26.1.1, 26.1, 1.21.1 and 1.20.1. Here's the thing, those are separate entries, so don't assume anything in between is covered.
The project marks server side as required and client side as unsupported. In plain terms, the work happens on the server.
The license is the GNU Lesser General Public License v3.0 only.
