Matching Mod Versions to Your Forge Install

Three things have to line up

Most "the mod does not work" problems are a version mismatch, and there are only three things to check.

• The Minecraft version. A mod built for 1.20.1 will not load on 1.21. This is the one people get wrong most often, because a download page may offer many versions and default to the newest.
• The loader. Forge, NeoForge and Fabric are different loaders and their mods are not interchangeable. A Fabric jar in a Forge mods folder does nothing at all.
• The Forge version itself. Within one Minecraft version, a mod sometimes needs a minimum Forge build. Installing a recent Forge for that Minecraft version is normally enough.

Reading a mod's filename

Most mod files carry all of this in the name, in some order: the mod's name, the Minecraft version, and often the loader. A file like SomeMod-1.20.1-forge-3.2.0.jar is telling you it is for Minecraft 1.20.1, on Forge, and is version 3.2.0 of the mod. When the name is not clear, the download page's own version list is.

Libraries and dependencies

Some mods need a second mod to work — a library or API. Those are listed in the Requires box on the download page, and they follow the same rules: same Minecraft version, same loader. If a required library is missing, the game stops during startup and names what it wanted, so you do not have to guess.

When you update

Updating Minecraft means updating everything. Moving a modded setup to a newer Minecraft version requires a new Forge install for that version and a matching version of every mod you use. If even one mod has not been updated yet, the usual choice is to stay on the older version until it is.

This is why separate game directories per setup are worth the trouble — an older pack keeps working untouched while you build the new one beside it.