Why is my Minecraft mod not loading?

Most often the mod is in the wrong folder, made for another loader (Fabric vs. Forge) or Minecraft version, or a required dependency like Fabric API is missing. Start the game through the mod loader, put the .jar into the mods folder of that instance and install all dependencies.

Where do datapacks go?

Datapacks belong to a world: saves/ /datapacks in singleplayer, or /datapacks on a server. Run /reload afterwards and check /datapack list. The zip must have pack.mcmeta at its top level.

Which Java version does Minecraft need?

Minecraft 26.1 and newer needs Java 25, 1.20.5 to 1.21.x Java 21, 1.18 to 1.20.4 Java 17, 1.17 Java 16, and 1.16 and older Java 8.

How do I find out which mod crashes my game?

Read the crash report or upload logs/latest.log to mclo.gs. If that does not name it, move half of your mods out, start the game and keep halving until one mod is left.

Where can I get help with Jodek's datapacks and mods?

Join the Discord linked at the end of the guide and include what you tried and your log.

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Why is my Minecraft mod not loading?: Most often the mod is in the wrong folder, made for another loader (Fabric vs. Forge) or Minecraft version, or a required dependency like Fabric API is missing. Start the game through the mod loader, put the .jar into the mods folder of that instance and install all dependencies.
Where do datapacks go?: Datapacks belong to a world: saves/<your world>/datapacks in singleplayer, or <world folder>/datapacks on a server. Run /reload afterwards and check /datapack list. The zip must have pack.mcmeta at its top level.
Which Java version does Minecraft need?: Minecraft 26.1 and newer needs Java 25, 1.20.5 to 1.21.x Java 21, 1.18 to 1.20.4 Java 17, 1.17 Java 16, and 1.16 and older Java 8.
How do I find out which mod crashes my game?: Read the crash report or upload logs/latest.log to mclo.gs. If that does not name it, move half of your mods out, start the game and keep halving until one mod is left.
Where can I get help with Jodek's datapacks and mods?: Join the Discord linked at the end of the guide and include what you tried and your log.

Words explained

Launcher: The app you start Minecraft with, like the official Minecraft Launcher, the Modrinth App, Prism Launcher or CurseForge.
Instance / profile: A separate Minecraft setup inside your launcher, with its own version, loader and mods folder. The Modrinth App and Prism call it an instance, the official launcher an installation or profile.
Loader (mod loader): The program that lets Minecraft run mods: Fabric, Forge, NeoForge or Quilt. A mod only works with the loader it was made for.
Vanilla: Minecraft as it comes, without a mod loader or mods.
.jar file: The file type mods and plugins come in. It goes into the mods or plugins folder as it is, without unzipping it.
Dependency: Another mod that a mod needs to work, for example Fabric API. The mod page lists them, usually under "Dependencies".
Log (latest.log): A text file where the game writes down what it does. It is in the logs folder of your instance or server as latest.log. Errors in it often name the broken mod.
Crash report: A file the game writes when it crashes, in the crash-reports folder. The first lines usually say what went wrong.
mclo.gs: A free website where you upload a log and get a short link to share when you ask for help.
pack.mcmeta: A small file every datapack and resource pack needs at the top of its zip. Without it, Minecraft ignores the pack.
/reload and /datapack list: Commands you type in the chat. /reload loads datapack changes in an open world, /datapack list shows which datapacks are turned on. You need cheats or operator rights for them.
Shader pack, Iris, OptiFine: A shader pack is the zip with the shader itself and goes into the shaderpacks folder. Iris and OptiFine are mods that make shader packs work.
Config: A settings file that a mod, plugin or modpack creates, usually in the config folder.
Console: The window or panel where a server shows its messages and where you can type commands without a slash.
Operator (op) and permissions: Operators are server admins who may run commands. Plugins often add permissions, which decide who may use a command; the plugin page lists them.
Paper, Spigot, Purpur: Server software that runs plugins. Plugins do not work in singleplayer or with mod loaders like Fabric.
RAM (memory): The memory your computer lends Minecraft while it runs. Big modpacks need more; you set it in your launcher.

Need the right versions of everything? The Modrinth Bundler picks them for you, dependencies included.