Aternos Mods Missing After Deleting? Fix the Crash
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You added a couple of mods on Aternos (say The Aether and Farmer's Delight), changed your mind, removed them, and now the game says they're missing or the server crashes. The mod is gone, so why is anything still asking for it?
Short answer: something still remembers the mod. It's one of four things: the mods in your own launcher, an addon or library that needed the mod, the world itself, or a player who logged out inside the mod's dimension. Where the message appears tells you which one. Back up first, then work through the table below.
Before you touch anything: back up
Open your server's Backups page on Aternos and make a backup now. Every fix below either changes the world or puts mods back, and the one mistake you can't undo is the server saving the world without the mod's content. If you have an older backup from before you installed the mods, keep it too.
Find your cause from where the message appears
| Where you see it | What's going on | Fix |
|---|---|---|
| On your screen when you try to join (the server is online) | Your launcher and the server have different mod lists. You probably still have Aether or Farmer's Delight in your own game, or a friend does. | Make the lists match (cause 1) |
| The server won't start; the log names a mod that "requires" or "depends on" another | You removed a mod that something else still needs, such as an addon or a library | Remove the addon too, or re-add what it needs (cause 2) |
| The server starts, but the log warns about missing entries and blocks or items from the mod are gone | The world was saved with that mod's content in it | Re-add the mod, or accept the loss on purpose (cause 3) |
| One player can't join, or spawns somewhere odd, everyone else is fine | That player logged out inside a dimension the mod added (The Aether is one) | See cause 4 |
To read the server log on Aternos, start the server and open the Log page. Scroll up from the bottom to the first line that says ERROR or names a mod ID: the last lines are usually the shutdown, not the cause.
Cause 1: your launcher still has the mods
This is the most common one. On a modded server, the mods on the server and in each player's launcher have to match (server-only mods are the exception). If you removed Farmer's Delight from the server but your CurseForge, Modrinth or Prism profile still has it, the game refuses to connect and tells you which mods differ.
Fix:
- Open the same profile you play on and remove the mods you removed from the server, plus any library they pulled in that nothing else uses.
- Make sure the profile's loader (Forge, NeoForge or Fabric) and Minecraft version match the server's Software page.
- Tell your friends to do the same. One player with an old profile gets the same error.
If you need the full list of what's on the server, it's on the Aternos Mods page. Our guide to adding mods on Aternos covers loaders, dependencies and what players need in their own launcher.
Cause 2: a leftover addon or library
Mods lean on each other. Two real examples, checked on Modrinth:
- The Aether (1.21.1, NeoForge, version 1.5.10) requires owo-lib and bundles Accessories and Cumulus. Removing The Aether and leaving owo-lib is usually harmless: a library on its own does nothing. Removing owo-lib while The Aether stays is a guaranteed crash at startup.
- Farmer's Delight Refabricated (the Fabric version, 3.6.30 for 26.3) requires Fabric API. Addons such as More Delight need Farmer's Delight in turn. If you removed Farmer's Delight but kept an addon, the server stops with a message naming the addon and what it needs. On Fabric the log says "Incompatible mods found!" followed by the details.
Fix: read the log line that names the missing mod, then either remove the addon that's asking for it, or install the missing mod again. Restart after each change, one change at a time, so you know which one fixed it.
Cause 3: the world remembers the mod
When a modded world saves, it stores the mod's blocks, items and entities. Forge and NeoForge also keep a list of the mod content the world uses and compare it with what's installed each time the world loads. Take a mod away and the server reports missing entries. Depending on the loader and version, it either carries on and deletes that content (mod blocks turn to air, mod items vanish from chests and inventories) or refuses to continue.
You have two honest options:
- Put the mod back at the same version. This is the only way to keep the content. Install the exact version you had before, start the server, and the world loads as it was. Then remove things properly if you still want to: empty the mod's chests and machines first.
- Accept the loss on purpose. If you only had the mod for a few minutes, there may be almost nothing of it in the world. Keep the backup you just made, let the server load without the mod, and check that the world works.
If neither works, restore the backup from before you installed the mods. You lose anything built since then, but the world is clean.
Cause 4: a player is stuck in a mod's dimension
The Aether adds its own dimension. If a player logged out inside it and you then removed the mod, that player's saved position points at a world that no longer exists. Some setups move them back to spawn; on others they get an error while everyone else plays normally.
Fix: the clean way is to put the mod back, have that player walk out through a portal and log out in the Overworld, then remove the mod again. If that's not possible, restore a backup from before they entered the dimension. Next time, ask everyone to leave mod dimensions before you remove a mod.
How to remove a mod safely next time
- Ask players to empty mod chests and machines and to leave any mod dimension.
- Stop the server and make a backup.
- Remove the mod and the addons that need it. Leave libraries other mods still use.
- Start the server, read the log, then join with a launcher profile that matches.
- Remove the same mods from every player's profile.
When Aternos itself is the limit
Removing a mod is harder than it needs to be when you can't see or change the server's files directly: Aternos installs mods from its own library, so you can only put back a version of a mod that the library offers, and you can't upload the exact jar you had. (More on that in can you upload custom mods to Aternos.)
On a host where you control the files, the same fix is: stop the server, delete or add the .jar in the mods folder, start it again. On Packyard, the Fabric, NeoForge and Forge servers (no modpack) work that way: upload or delete mods in the panel's file manager or over SFTP, on the Minecraft version you pick. You can make a backup yourself in the panel before each change and restore it in one click if it goes wrong, and daily backups are on top of that. The server stays on, with a permanent address your friends don't have to re-type.
Packyard is $1.50 per GB of RAM a month, $5 minimum (3 GB). 4 GB, our pick for a lightly modded server, is $6. Prices are in USD plus applicable taxes. Available in the US and Canada (not Quebec); servers run in US West. How Packyard compares with Aternos, and how to move your Aternos world over.
Start a Fabric server where you control the mods folder
Aternos is a trademark of its owner; Packyard is not affiliated with Aternos. The Aether and Farmer's Delight belong to their authors. Packyard is not an official Minecraft product and is not affiliated with Mojang or Microsoft.
FAQ
Why does my Aternos server say a mod is missing when I deleted it?
Usually because your own launcher still has the mod, or another mod on the server still needs it. Read where the message appears: on your join screen it's your launcher; in the server log it's a leftover addon or the world.
Will removing a mod delete things from my world?
Yes, anything that came from that mod: its blocks, items, mobs and dimensions. Vanilla blocks and items stay. Back up first.
Can I get my world back after removing a mod?
Reinstall the same version of the mod before the world is saved again, or restore a backup made before the change.
Do my friends need to remove the mod too?
Yes. On a modded server every player's mod list has to match the server's, apart from server-only mods.
How do I find which mod is causing the crash?
Open the server log and look for the first ERROR line or a mod ID near the start of the crash. The mod named there, or the mod it says it needs, is where to start.
More guides and posts on the Packyard blog.