You add a handful of mods to your Minecraft server, press start, and it stops after a few seconds
with “the game closed”. Which file? You don’t know, so you start removing them one by one, or you give
up. That is what happened to one of our customers on 1 October: 102 files uploaded into mods/ after
a crash, and the server was never started again.
Most of these failures come from a few mistakes that can be recognised before starting, or named right after.
When you upload: a warning, before you start
On a Forge, NeoForge, Fabric or Quilt server, the file manager now looks at what you have just dropped into the mods folder and points out three kinds of files:
- An archive uploaded as-is (
.zip,.rar,.7z…). The server only loads.jarfiles and unpacks nothing: extract it on your computer, upload the.jarfiles inside, then delete the archive. - A mod built for the other loader, such as the Fabric version of a mod on a Forge server. Replace it with the version for your loader, same Minecraft version.
- A rendering mod (OptiFine, Sodium, Iris, Oculus, Embeddium, Rubidium). These belong in each player’s game, not on the server: remove them from the server and keep them on your PC.
It is only a warning. Nothing is blocked, and if you know what you are doing, you can start anyway.
When it fails: the reason, on your server page
Some mods are made for the player’s game and go looking for its display: a window, rendering, the interface. A server has none of that, so it stops while loading. That is what we saw on 5 October with Distant Horizons on a Fabric server.
Now the start is cancelled with a clear message: a mod is meant for the player’s game. On Fabric, the message gives the mod’s name. Your world is not changed.
And the notice explaining why the last start failed is back at the top of your server page. It had disappeared when the page was redesigned, so a failure that had been understood was no longer shown to you.
What this doesn’t solve
- The upload warning only reads file names. A mod with an unclear name gets through, and a multi-loader mod may be flagged for nothing. That is why we warn instead of blocking.
- On Forge and NeoForge, the mod isn’t always named. The message explains what to look for, but the logs don’t always say which file it is.
- Not every crash is recognised. A missing dependency or a mod made for another Minecraft version can still end with “the game closed”. In that case, remove the last mods you added first.