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What "Missing or unsupported mandatory dependencies" means
"Missing or unsupported mandatory dependencies" means at least one mod on the server needs another mod that is not there, or not in a version it accepts. Most mods lean on a library: a shared mod with code that several other mods use, such as GeckoLib for animations or Curios for extra equipment slots. Each mod declares which libraries it needs and from which version. Before anything else loads, NeoForge and Forge check those declarations, and when one fails they stop with a list of everything that is wrong.
Console, NeoForge on Minecraft 1.21.1
[main/ERROR] [net.neoforged.fml.loading.ModSorter/LOADING]: Missing or unsupported mandatory dependencies:
[main/FATAL] [net.neoforged.fml.ModLoader/CORE]: Error during pre-loading phase: Mod jeresources requires jei 16.0.0 or above
Currently, jei is not installed
net.neoforged.fml.ModLoadingException: Loading errors encountered:
- Mod jeresources requires jei 16.0.0 or above
Currently, jei is not installedThe first line is only a heading. The lines that matter come right after it, one pair per problem: a requires line and a Currently line. A server with a dozen mods missing their library prints a dozen pairs, and you can fix all of them in one go before the next start. The stack trace under ModLoadingException adds nothing new, so you can skip it.
How to read "Mod X requires Y 1.2.0 or above"
Every requires line has the same three parts: the mod that has the problem, the mod it needs, and the versions it accepts. In Mod jeresources requires jei 16.0.0 or above, the mod Just Enough Resources cannot start because it needs Just Enough Items (jei), version 16.0.0 or newer. The line below says what the server has right now.
| Version text | What the mod accepts |
|---|---|
2.4.1 or above | 2.4.1 or any newer version |
9.3.14 or above, and below 9.4.0 | From 9.3.14 up to, but not including, 9.4.0 |
9.3.14 | Exactly that version, nothing else |
1 or above | Any version from 1 up, so in practice any release |
| The Currently line | What to do |
|---|---|
Currently, jei is not installed | Add the mod. It is not on the server at all. |
Currently, jei is 15.2.0.27 | The mod is there but too old or too new. Replace it with a version inside the range. |
Reason for the dependency: ... | The mod author's own note on why it is needed. Read it; it sometimes names the exact release. |
The name after requires can also be neoforge, forge or minecraft. Mod X requires neoforge 21.1.200 or above means the loader itself is too old for that mod, and requires minecraft 1.21.1 means the mod was made for another Minecraft version. In those cases you change the server, not the mods: a newer NeoForge or Forge build for the same Minecraft version, or the mod's release for your Minecraft version.
The name in the error is a mod ID, not the mod's title
The loader writes the mod ID: the short, lower case name a mod uses inside the game. It often differs from the title on the download page, which is why searching for cloth_config or puzzleslib can feel like a dead end. These are the libraries we see missing most often on modded servers, with the title to search for:
| Mod ID in the error | Search for | What it is |
|---|---|---|
jei | Just Enough Items | Recipe viewer; other mods add their own pages to it |
geckolib | GeckoLib | Animation library for mobs, armor and items |
curios | Curios API | Extra equipment slots for rings, belts and backpacks |
architectury | Architectury API | Shared code for mods made for several loaders |
cloth_config | Cloth Config API | Settings screens and config files |
collective | Collective | Shared code for a large family of small mods |
puzzleslib | Puzzles Lib | Shared code for another family of mods |
citadel | Citadel | Library behind several creature mods |
playeranimator | playerAnimator | Player animations for combat and emote mods |
sophisticatedcore | Sophisticated Core | Base for Sophisticated Backpacks and Storage |
balm | Balm | Shared code for a group of utility mods |
jade | Jade | The tooltip that names the block you look at |
Take the release for your loader (NeoForge or Forge, not Fabric) and your Minecraft version. A library for the wrong loader is just another error on the next start.
Not every missing name is a library. When the needed mod is a full content mod, such as a whole Pixelmon or Croptopia, the error means you added an add-on without the mod it belongs to. Install the main mod, or take the add-on out again.
Mod loading failures have occurred; consult the issue messages for more details
"Mod loading failures have occurred; consult the issue messages for more details" is the description NeoForge writes into the crash report when mods could not load. The issue messages it refers to are a few lines lower in the same report, one block per mod, and they hold the same requires and Currently pairs as the console.
crash-reports/crash-<date>-server.txt
Description: Mod loading failures have occurred; consult the issue messages for more details
net.neoforged.neoforge.logging.CrashReportExtender$ModLoadingCrashException: Mod loading has failed
-- Mod loading issue for: treeharvester --
Failure message: Mod treeharvester requires collective 8.57 or above
Currently, collective is not installedOn Forge for 1.20.1 the console shows the same message with colour codes still in it, because the text was made for a coloured screen: Mod §eemotecraft§r requires §6playeranimator§r §o0.2.0 or above§r. Read past the § marks: the mod is emotecraft, the missing library is playeranimator.
A player whose own NeoForge game has the same problem sees these lines on a screen titled Error loading mods. On the server, crash reports are in the crash-reports folder on the Files tab, newest at the bottom. The guide to crash reports and logs explains the rest of the report, in case it does not start with this description.
How to fix missing mod dependencies on your server
List every pair
Copy all
requireslines from the console or the crash report. Several mods often need the same library; you only install it once.Find each mod by its title
Look up the mod ID in the table above, or on the page of the mod that needs it: download pages list required mods under Dependencies. Pick the release for your loader and Minecraft version, inside the version range from the error.
Install it on the server
On the Mods tab, search the verified catalog and choose Verify & install. It adds the mod together with the required mods that are not on your server yet. For a file you downloaded yourself, stop the server and upload the jar to the
modsfolder on the Files tab.Start, and repeat if needed
Start the server and read the console again. A library can have libraries of its own, so a second, shorter list is normal. When the console reaches
Done, every dependency is met.
Players need the same mods
Libraries that a content mod needs on the server are usually needed on the player's side too. Add them to the modpack or the mod list your players use, or they will see the same error when they start their game. Joining a modded server covers that side.
When the mod is installed but the version is wrong
A Currently line with a version number instead of not installed means the mod is there, just not a version the other mod accepts. Two things cause this. Either the library is older than the range, which you fix by updating it, or the range has an upper limit (and below 9.4.0) and your library is newer, which you fix by taking the release just below that limit.
When two mods want ranges that do not overlap, no single version can satisfy both, and one of them fails whichever version you pick. For libraries that mods carry inside their own jar, NeoForge says so directly with Some mods have requested conflicting versions of. Either way, one of the two mods has to change: update the one that is behind, or remove the one you can live without.
only supports and is incompatible with
NeoForge has two more lines in the same family. Mod X only supports Y ... is about an optional mod: X can run without Y, but not with the version of Y you have, so update Y or remove it. Mod X is incompatible with Y means the author of X marked Y as something that breaks it, and one of the two has to go. The line The reason is: gives the author's explanation, or says that none was provided.
Written and checked by the Lodehost team, last reviewed on 7 November 2026.
