Logs are an essential part when it comes to debugging your server and figuring what went wrong. This page will show some basic logging examples and will try to explain what you can do to fix your issues, when encountering them.


Whenever you encounter a crash or warning make sure you set SpongeForge or SpongeVanilla up correctly. Here’s a short checklist to help you out. If you’re unsure on how to acquire the information needed, have a look at the Log Files page. It explains how you get the desired answers out of your log files.

Is Java 8 installed and is Sponge using it?

Sponge requires Java 8 and will crash when using Java 7 or older.

Are there any other coremods installed?

Some coremods modify Forge or Minecraft in a way that makes it impossible to run SpongeForge properly. If you have coremods installed and Sponge crashes, try to remove them and test again. Please report any incompatible coremods on GitHub. This allows staff to solve these issues as soon as possible.

Is every plugin you’re using built against your desired Sponge build?

SpongeAPI is subject to change sometimes. When you try to use an older plugin on the most recent Sponge build and a crash occurs, try downgrading Sponge or contact the plugin author to get an updated plugin. If you’re on an older Sponge build and a recent plugin crashes, try to update Sponge first. If that doesn’t fix the issue, contact the plugin author and ask for a fix.

Separating a faulty plugin

If the problem still persists, try to remove all plugins and re-add them one by one while trying to start the server every time you added a plugin.

If you’re still unsure why and what exactly crashed, have a look at your crashlog. Some common crashes and common solutions are listed below.


If you encounter a bug it is usually a good idea to create a backup first, then try to reproduce it, then narrow it down by removing mods. Only then should you report the error. If the error occurs in the absence of Sponge plugins, try removing SpongeForge. If the error persists its not related to Sponge. Its usually a good idea to report bugs to the mod authors first as they have good knowledge of the parts of code they are working with. However you can always contact us for questions. For more information see Reporting Bugs.

General Warnings

A common source of errors and bugs is a version mismatch between either SpongeForge and Forge or SpongeForge and Plugins. First we’ll have a look at the general warning Forge gives us upon crashing:

WARNING: coremods are present:
   SpongeForge (sponge-1.8-1521-2.1DEV-750.jar)
Contact their authors BEFORE contacting forge

This isn’t a bug or error, it’s just Forge telling you that a Coremod (here: SpongeForge) is installed. Forge advises you to contact the Sponge developers first, before asking the Forge support for help. Nothing to worry about.

Common Exceptions

Here are some common exceptions and some reasons why you might encounter them.


If you encountered a crash, error or any other malfunction not listed here, please report it on the Sponge Forums or on GitHub. This will help others, who are running into the same issue.

Mismatched SpongeForge and Forge

[12:59:21] [main/ERROR] [mixin/]: @Mixin target$NeighborNotifyEvent was not found mixins.forge.core.json:event.block.MixinEventNotifyNeighborBlock

This is a common crash when you try to run SpongeForge on the wrong Forge build. Note that the target/Mixin can vary. Always match Forge against SpongeForge! If you’re unsure which version of Forge is required and you already got your SpongeForge build, take a look at: Installing SpongeForge

Other common errors

Caused by: java.lang.ClassNotFoundException: org.spongepowered.api.event.state.ServerStartedEvent
Caused by: java.lang.NullPointerException

The first error indicates that a Class is missing, the second is a NullPointer Exception which indicated that the plugin you’re trying to use relies on missing parameters. This happens when you try to run and older plugin on a newer SpongeForge or SpongeVanilla build and vice versa.

java.lang.AbstractMethodError: net.minecraft.entity.player.EntityPlayerMP.getTabList()Lorg/spongepowered/api/entity/living/player/tab/TabList;
at (...)

An AbstractMethodError occurs when a plugin tries to call a method which isn’t implemented yet. Please check if you’re running the most current build of Sponge and update if a newer version is available. If the problem still exists, either report it on the official Issuetracker, on the forums or on IRC. You can request the implementation of the missing feature too.

[Server thread/INFO]: Starting minecraft server version 1.8
[Server thread/ERROR]: Encountered an unexpected exception
java.lang.NoClassDefFoundError: org/spongepowered/api/event/game/state/GameStartingServerEvent


Read the full example crashlog here: SpongeForge 575 crashlog with a plugin built against build 750

A NoClassDefFoundError occurs when the plugin tries to access a class that isn’t on the classpath. This happens when the API got adjusted or refactored lately and you’re trying to run an older plugin on a newer build of Sponge and vice versa. Always try to use the correct version! Either ask the Plugin author which Sponge version he builds against or try updating/downgrading your SpongeForge or SpongeVanilla to solve this.

Exceptions at Runtime

There are two kinds of errors that may occur on modded servers:

  • Plugin internal errors, such as NullPointerExceptions during command execution. These errors are logged using the standard Java error handler.
  • Errors during the ticking of worlds or entities. Sponge prints out more structured errors to provide as much information as possible.

Before we look into the details of what caused the exception, make sure that you read all of the error report. Sometimes the error is explained in the error report itself (or a few lines above or below it); sometimes it is indicated by a warning during startup.

The following stacktrace shows an example of this special handling (excluding the line prefix with time and severity):

/*                                           Exception occurred during a PhaseState                                           */
/* Sponge's tracking system makes a best effort to not throw exceptions randomly                                              */
/* but sometimes it is inevitable. In most cases, something else triggered this                                               */
/* exception and Sponge prevented a crash by catching it. The following stacktrace                                            */
/* can be used to help pinpoint the cause.                                                                                    */
/* The PhaseState having an exception: EntityTickPhase                                                                        */
/* The PhaseContext:                                                                                                          */
/*     - Owner: EntityPlayerMP['SomePlayer'/270, l='world', x=119,62, y=82,00, z=260,21]                                      */
/*     - Source: EntityCreeper['Creeper'/346, l='world', x=119,50, y=82,00, z=258,50]                                         */
/*     - CapturedBlockPosition: CaptureBlockPos{pos=null, world=Optional.empty}                                               */
/* org.spongepowered.asm.util.PrettyPrinter@56ec63ef                                                                          */
/* StackTrace:                                                                                                                */
/* java.lang.NullPointerException: null                                                                                       */
/*     net.minecraft.util.math.BlockPos.<init>(SourceFile:41)                                                                 */
/*     net.minecraft.pathfinding.PathNavigateGround.func_75494_a(SourceFile:73)                                               */
/*     net.minecraft.pathfinding.PathNavigate.func_75497_a(SourceFile:147)                                                    */
/*     com.example.extendedaiplugin.BrokenAITask.start(                                                  */
/* */
/*                                                     */
/*     net.minecraft.entity.EntityLiving.func_70626_be(                                                 */
/*     net.minecraft.entity.EntityLivingBase.func_70636_d(                                         */
/*     net.minecraft.entity.EntityLiving.func_70636_d(                                                  */
/*                                                 */
/*     net.minecraft.entity.EntityLivingBase.func_70071_h_(                                        */
/*     net.minecraft.entity.EntityLiving.func_70071_h_(                                                 */
/*                                                */
/*                                       */
/*     org.spongepowered.common.event.tracking.TrackingUtil.tickEntity(                                 */
/*$onCallEntityUpdate$zlo000(                              */
/*                                                                */
/*                                                     */
/*                                                                */
/*                                                                */
/*                                                    */
/*     net.minecraft.server.MinecraftServer.func_71190_q(                                            */
/*     net.minecraft.server.dedicated.DedicatedServer.func_71190_q(                                  */
/*     net.minecraft.server.MinecraftServer.func_71217_p(                                            */
/*                                                     */
/* Source)                                                                                   */
/*  Phases Remaining:                                                                                                         */
/*                                                                                                                            */
/* Minecraft : 1.12.2                                                                                                         */
/* SpongeAPI : 7.1.0-SNAPSHOT-7105dfc                                                                                         */
/* SpongeForge : 1.12.2-2705-7.1.0-BETA-3361                                                                                  */
/* Minecraft Forge :                                                                                             */

This stacktrace contains the most important version numbers, as well some information about the phase the server was in. In this case a NullPointerException has been thrown during EntityTickPhase. At this point it’s important to check which plugins are involved with the crash. This requires some research as you have to match the package names with mod names; checking the Caused by blocks may also help.

  • java classes can be ignored during the error search.
  • net.minecraft is the vanilla Minecraft code. If only these elements are present, it’s either a Minecraft bug or a coremod.
  • org.spongepowered is from Sponge itself, having only these and Minecraft packages present usually indicates a Sponge bug (or another coremod being present).
  • Other classes have to be mapped to their mods by hand. In this case there is this entry com.example.extendedaiplugin; Java projects are usually named following this format groupId.groupId.artifactId. The group is usually a domain backwards; in this case, followed by the name of the project also known as artifact, for more information on package naming in Java you can refer to its official docs. This plugin is probably called extendedaiplugin, when in doubt, searching the web for the full package name can help.


Be careful when coremods are present. It can mean that, although a Minecraft class was reported as the cause, it does not mean the code executed is necessarily part of the Minecraft source, and could have been added by a third party. You can check your logs for loaded coremods and potentially find the culprit by removing them one by one. Be warned the issue may only occur when certain coremods are loaded at the same time.