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Install a mod without breaking your world
The game version, mod loader, and dependencies must all match. Follow this short sequence before opening an existing world.
Safe installation sequence
Back up the world
Copy the world folder from .minecraft/saves, especially for mods that add entities, blocks, or world generation.
Match the game version
A mod for 1.21.5 will usually not run on 1.21.1. Check both the launcher profile and the exact file page.
Choose the required loader
Fabric, Forge, and NeoForge are separate platforms. Install exactly the loader requested by the mod.
Add the file and dependencies
Move the .jar into .minecraft/mods without extracting it. Add Fabric API, GeckoLib, or other required libraries.
For AI mods: enter API keys only in a trusted mod’s settings. With Ollama, remember that Minecraft and the model consume memory at the same time.