How to Install Naturalist Mod on NeoForge 1.21.1
A reliable NeoForge setup starts by separating three things that are often confused: the Minecraft version, the loader version and the Naturalist file itself. For this site, the supplied download URL points to a 1.21.1-NeoForge source branch ZIP, which is not the same as a packaged mod JAR.
Step 1: confirm Minecraft 1.21.1
Open the profile you plan to modify and confirm it is actually Minecraft Java 1.21.1. A nearby version number is not a safe substitute. Mods are built against specific APIs and game internals, so version matching is part of installation, not a later troubleshooting step.
Step 2: use a compatible NeoForge profile
Naturalist must be paired with the loader family named by the build. If your profile is Fabric, do not place a NeoForge build into it. If your profile is NeoForge, record the loader version before changing anything else so you can reproduce the setup if needed.
Step 3: distinguish source ZIP from packaged JAR
The main button on this website uses the provided GitHub source-archive link for the 1.21.1-NeoForge branch. Source archives are useful for code review or development, but regular players generally need a packaged release JAR. Do not simply rename a ZIP to .jar; that does not turn source code into a compiled mod.
Step 4: install the packaged build
Once you have a Naturalist JAR that explicitly matches Minecraft 1.21.1 and NeoForge, place it in the mods folder used by that profile. Keep required dependencies with the same game and loader compatibility. Start the game and verify Naturalist appears in the loaded mod list before opening an important world.
Step 5: test before committing a world
Create a temporary test world or copy an existing one. Confirm that the game loads, entities behave normally and no immediate errors appear. Only then use the setup with the original world. If it fails, remove unrelated mods and retest with the smallest possible set.