Fix "Missing Dependency" and Mod Conflict Errors

A "missing dependency" error means a mod you installed needs another mod (or a specific loader/version) that isn't present on your server, and it will refuse to start until that gap is filled. Check the Console for the exact mod name it's missing, install that dependency through Mods Installer, and restart.

Symptoms

• Server won't start after adding a new mod
• Server won't start after removing a mod (something else needed it)
• Blocks not breaking, items not dropping, or other odd behavior after mod changes
• Crash logs mentioning a specific missing mod, wrong Forge/NeoForge variant, or "FML" errors
• Plugin appears installed but simply doesn't load on your version

Why this happens

Mods and plugins are not interchangeable, and mods themselves often depend on other mods:

• Missing library mods. Many mods (Supplementaries, Accessorify, Rechiseled, create-radar addons) require a separate "lib" mod like Moonlight Lib, fzzy_config, or corelib. Skip the library and the main mod won't load.
• Deleting a mod others rely on. If you remove a mod that other installed mods depend on, those other mods break too: this cascades quickly in dependency-heavy packs.
• Wrong loader variant. Forge, Fabric, and NeoForge builds of the same mod are not interchangeable. Installing the Fabric build of a mod on a NeoForge server (or vice versa) throws dependency-style errors.
• Client-side-only mods installed on the server. Mods like Sodium or Hold My Items are client-only. They don't belong on the server and won't fix anything if added there.
• Plugins vs mods confusion. Plugins only run on Paper/Spigot loaders and only work with specific server versions: a plugin built for an older version simply won't load on a newer one, and no mod-side fix will help.
• Version mismatches after upgrades. Changing your Minecraft version can suddenly make mods that used to work incompatible.

Always take a backup before adding, removing, or updating mods. Cascading dependency errors are common, and a backup lets you roll straight back to a known-working state instead of troubleshooting under pressure.

How to fix it

1. Open Console and read the startup error: it names the exact missing mod or dependency.
2. Search that dependency's name in Mods Installer and install it, matching your exact loader (Forge/Fabric/NeoForge) and server version.
3. If you recently removed a mod, check whether other installed mods needed it: reinstall it if so, or remove the dependents too.
4. Confirm you haven't installed a client-side-only mod on the server; those belong only in the player's launcher, not the server's mod list.
5. If a plugin isn't loading, confirm it via Plugin Installer and check whether it supports your current server version: downgrading the server version is sometimes the fix, not the mod list.
6. If errors persist after a version change, check that every mod is built for the Minecraft version your server now runs.
7. Restart the server and re-check Console for a clean startup with no dependency errors.
8. Add mods back one at a time if you're rebuilding from scratch, testing a restart after each addition.

For details on reading crash output specifically, see Minecraft Server Won't Start: How to Read the Crash Log. If you're building a pack from scratch instead of patching one, use How to Install a Modpack on Your Minecraft Server so dependencies are bundled correctly. Switching loaders or versions to match a mod or plugin's requirements is covered in How to Change Your Minecraft Server Version, and for Paper-only issues see How to Install Plugins on a Spigot or Paper Server.

Still stuck?

If the Console error doesn't clearly name the missing dependency, or you've matched every loader/version and it still won't boot, open a support ticket with your crash log attached, our team can trace the exact mod chain that's failing.