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“Exception in server tick loop” is a crash wrapper, not a diagnosis. The correct fix depends on the first meaningful Caused by: entry in your crash report or latest.log. It can indicate an old server’s malformed JSON list, an incompatible mod or mixin, a broken dimension or chunk, a failed world upgrade, or an installation and Java problem. Back up the world, capture the complete trace, and follow only the branch that matches the named file, mod, dimension, or data.
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What the error actually means
Minecraft’s server tick loop is the repeating process that advances world time, entities, block updates, scheduled tasks, and player actions. When an exception escapes that loop, Minecraft stops and writes a crash report. The headline is shared by unrelated failures, so reinstalling Java, adding memory, or deleting configuration files is not a universal remedy.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallMojang’s issue tracker contains materially different examples under this same description. One report concerns an unregistered dimension type; another records a Superflat-world upgrade failure involving biome decoration. Older server documentation describes a separate NullPointerException in net.minecraft.server.v1_7_R3.JsonList.load(JsonList.java:171), where list files are implicated. These cases require different recoveries.
Do this before changing anything
- Stop the game or server. Do not keep restarting a world that may be writing damaged data.
- Make a backup. In Minecraft: Java Edition, open Edit World → Make Backup. The resulting ZIP includes the backup date and is stored in the backups folder. For a dedicated server, stop the process and copy the entire world directory, server properties, and configuration folders to a separate location.
- Save the evidence. Keep the crash report and
latest.log. Search from the top for the firstCaused by:, then read down to the deepest package name, mod ID, file, dimension, chunk, entity, or player reference. - Record the environment. Note the Minecraft version, loader (Forge, Fabric, NeoForge, or none), Java version, server JAR, installed mods, and whether the crash occurs in one world or every world.
- Choose one branch below. Make one reversible change at a time so you can tell which action changed the result.
Use the stack trace to choose the right branch
| What the deepest trace names | Most likely area | First safe test |
|---|---|---|
JsonList.load, ops.json, whitelist.json, or usercache.json |
Older server list-file failure | Back up, then recreate only the named JSON-list files |
| Forge, Fabric, NeoForge, a mod ID, mixin, or config parser | Mod, loader, mixin, or configuration incompatibility | Disable or roll back the named component and test the same version in a clean profile |
| Dimension type, biome decoration, chunk generation, entity data, or one world | World, dimension, chunk, or upgrade data | Test a copy of the backup and create a new world on the same game and mod versions |
| Launcher files, Java classes, memory allocation, or every installation | Installation, Java, or environmental problem | Build a clean installation with the same game version, then verify Java and memory settings |
The table is a decision aid, not a substitute for the trace. If the log identifies a mod, do not delete world files. If it identifies a world-generation object, do not assume that reinstalling Java will repair it.
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Branch A: repair the old JSON-list failure
When this branch applies
Use this procedure only when the stack trace matches the older pattern java.lang.NullPointerException: Exception in server tick loop at net.minecraft.server.v1_7_R3.JsonList.load(JsonList.java:171), or explicitly points to the server’s operator, whitelist, or user-cache JSON files. This is associated with much older server software; the same headline on a modern installation does not prove that these files are at fault.
Recreate the files
- Stop the server completely and wait until the Java process exits.
- Open the server directory in your file manager.
- Confirm that your backup is outside the server directory.
- Move
ops.json,whitelist.json, andusercache.jsonto a quarantine folder rather than permanently deleting them. If one of the files does not exist, leave the others untouched unless the trace names them. - Start the server again. The server should create fresh list files.
- Re-add operators and whitelist entries through the server’s normal commands or management interface. Do not paste old JSON back until the server starts normally; a malformed entry can recreate the crash.
Moving all three files is the documented sequence for this exact old-server pattern, but it is not a general Minecraft repair. If the same trace returns, restore the quarantined copies, keep the backup, and investigate the old server build or its Java compatibility rather than repeatedly deleting files.
Branch B: isolate a mod, loader, mixin, or configuration
Read the named component
A trace that ends in a Forge, Fabric, or NeoForge class, a mixin transformation, a mod ID, or a configuration parser points to the modded runtime. Look for the first non-loader package below Caused by:; that is often more useful than the final generic tick-loop line. Configuration errors may include a path or key that identifies the file to inspect.
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Test without destroying the world
- Duplicate the instance or server profile and point the copy at a backup of the world.
- Keep the Minecraft version, loader version, Java version, and launch arguments unchanged for the first test.
- Disable the named mod or revert it to the version required by the pack. If the loader identifies a mixin, disable the mod that supplies that mixin rather than editing generated classes.
- Launch the copied profile and reproduce the same action: loading the world, entering a dimension, or joining with the affected player.
- If it works, re-enable disabled components in small groups. When the crash returns, split that group and test again until one component or combination is isolated.
- Check the isolated mod’s documented Minecraft and loader compatibility, then update or roll back only that component.
Minecraft Help states that modding is not officially supported by Minecraft Support and that mods are third-party software that can make the game malfunction. Once a clean profile confirms a mod-related cause, the mod author or mod-pack maintainer is the appropriate escalation path. Keep the crash report, loader version, mod list, and reproduction steps when reporting it.
Branch C: repair or work around world and dimension failures
Recognize data-specific evidence
Choose this branch when the trace names a dimension type, biome decoration, chunk coordinates, terrain or chunk generation, entity NBT, a player UUID, or one particular world. A crash that occurs only while loading one save is especially significant. Mojang issue records document an unregistered dimension type and a Superflat-world upgrade crash tied to biome decoration. Those historical reports demonstrate that the same headline can come from world data and generation code, not from the launcher.
Use a copy for every experiment
- Leave the original backup untouched and make a working copy of the world.
- Use the same Minecraft version, loader, mods, and Java version that produced the crash. Changing several variables at once makes the result inconclusive.
- Create a new test world with the same profile. If the new world loads while the old one fails, the problem is likely tied to the original world, its upgrade path, or a dimension/chunk record.
- Check the trace for the dimension or chunk named at the time of failure. Avoid deleting region files, player data, or dimension folders unless a documented, targeted recovery tells you exactly what will be lost.
- If a newer mod or game version is suspected, test the copy after making a second backup. Keep the original version available so you can roll back.
Historical tracker entries list fix versions 1.16 Pre-release 3 for the unregistered-dimension report and 1.18 Pre-release 4 for the Superflat upgrade report. Those entries describe fixes for specific historical defects; they are not guarantees that every current server using those or later versions is unaffected.
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When a new world is the practical recovery
If only one save fails and repeated tests identify irreparable world data, a new world may be the safest way to resume play. Preserve the old save for later recovery, and copy structures or player data only after confirming that the relevant files are compatible with the current profile. A new world does not repair the damaged save; it is a controlled workaround.
Branch D: check installation, Java, and memory
Build a clean installation
Use this branch when the trace does not identify a mod or world object, the crash affects every world, or launcher files and Java classes appear in the deepest cause. Create a new Minecraft Java installation using the same game version. If the clean installation launches, troubleshoot downloaded mods and advanced settings from the old installation and copy defaults selectively rather than replacing the clean files wholesale.
Verify a dedicated server launch
- Install a current Java runtime appropriate for the Minecraft version.
- Confirm that the server JAR is the intended game version and that clients use the matching version.
- Open a terminal in the server directory, not a parent folder.
- Launch with the server command expected by the setup guide, such as
java -jar server.jar, replacing the filename with the actual JAR name. - Accept the EULA only through the server’s normal
eula.txtsetting and keep the launch output for comparison with the failing run.
A clean launch that still crashes while loading the same world points back toward world data or a version mismatch. A clean launch that works points toward the old installation’s mods, settings, or files.
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Change memory only when evidence supports it
Review JVM memory after the trace or launch output suggests an environmental allocation problem. Minecraft Help recommends editing the -Xmx value cautiously, backing up worlds first, and avoiding more than half of installed system RAM on a 64-bit system. On a 32-bit operating system, the documented maximum is 4 GB. These are limits and guidance from the 2026 support information, not a promise that allocating that amount is optimal for your pack.
Increase memory in small steps and monitor whether the same exception remains. More RAM cannot repair malformed JSON, an incompatible mod, an unregistered dimension, or corrupt world data. Excessive allocation can also leave too little memory for the operating system and other services.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Compare recovery options before you commit
| Option | Use it when | Reversibility | What it can establish |
|---|---|---|---|
| Move and recreate JSON list files | The trace points to JsonList.load and the old list-file pattern |
High if files are moved and backed up | Whether malformed operator, whitelist, or cache data caused the startup crash |
| Disable a named mod or mixin | The deepest package identifies a modded component | High in a copied profile | Whether the component or its interaction with another mod triggers the exception |
| Test a copied world or new world | The trace names a dimension, chunk, biome, entity, or one save | High when the original is preserved | Whether the failure is tied to world data rather than the installation |
| Clean installation | Every world or the base installation fails | High if the old profile remains intact | Whether downloaded files or advanced settings are involved |
| Increase JVM memory | Logs indicate allocation pressure or an environmental memory issue | High; restore the former value if needed | Whether the failure changes under a justified memory setting |
The safest option is the one that preserves the original world, uses the same Minecraft and Java versions, and changes only the component identified by the trace.
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Common mistakes that make the crash worse
- Deleting every configuration file: this removes evidence and may reset a working setup while leaving the real world or mod problem untouched.
- Reinstalling Java first: Java changes do not repair an unregistered dimension or malformed JSON list.
- Allocating all available RAM: Minecraft Help’s 64-bit guidance is no more than half of system RAM; 32-bit systems top out at 4 GB.
- Updating everything at once: simultaneous game, loader, mod, and Java changes prevent you from identifying the trigger.
- Editing the original save: always work from a dated backup or copied world.
- Relying on the headline: the phrase “server tick loop” contains no information about which subsystem failed; the nested cause does.
What to include when asking for help
Post the complete crash report or the relevant section of latest.log, including the first Caused by: and the deepest named class. Add the Minecraft version, loader and version, Java version, server JAR, mod list, operating system, whether the issue affects one world or all worlds, and the exact action that triggers it. Remove authentication tokens, server addresses, and other private details before sharing logs.
Quick wins for a faster PC:
Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →For a modded instance, contact the mod author or pack maintainer after reproducing the failure with a clean profile where appropriate. For an unmodded installation, use Minecraft’s official support channels and retain the backup and original logs.
Quick decision checklist
- Have you stopped the server and created a dated backup?
- Does the first meaningful cause name JSON lists, a mod or loader, world data, or the installation?
- Are you testing a copy while keeping the same Minecraft and Java versions?
- Did you change one variable and record the result?
- Have you avoided claiming that RAM, Java, or reinstalling Minecraft will fix a different named cause?
Once the trace identifies the failing subsystem, the error becomes a targeted repair rather than a generic server mystery. Preserve the original data, apply the narrow branch, and roll back the change if the evidence no longer points to it.
Quick Recap
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