What the message means
A server loads every data pack before it creates or opens the world. On a modded server that includes the data each mod ships inside its own jar, plus anything in world/datapacks/. If one file fails to parse, or names something that no installed mod registers, the dedicated server refuses to continue and prints Failed to load datapacks, can't proceed with server load.
Because the wrapper is the same every time, the useful information is the first ERROR line or Caused by: line above it. These are the shapes you are likely to find there.
| Line above it in the log | What it means | Where to look |
|---|---|---|
| JsonSyntaxException: Unknown item 'modid:thing' | A data file names an item that no installed mod registers. Block, fluid, biome, tag and enchantment are the same problem. | The mod whose id is before the colon, and the configs, quests or scripts that mention that id. |
| IllegalStateException: Overworld settings missing | The loaded mods and data packs do not define the overworld. | A removed world-generation mod or datapack. It has its own guide. |
| You must set <key> with selected configuration in your server.properties | A mod needs a server.properties setting the pack does not ship. | That mod's own documentation, for the value to use. |
| Couldn't parse data file | One data file is malformed or written for a different Minecraft version. | The file the line names, often inside world/datapacks/. |
Warning
Do not reset the world first. This error is usually one file or one missing mod, and the fix is to put the mod back or move that file out. Take a backup before you change anything.
If the line above says Overworld settings missing, the cause is world-generation data rather than a single bad file.
Read the Overworld settings missing guideHow to fix it
- Open logs/latest.log and scroll up from Failed to load datapacks to the first ERROR or Caused by: line. That line names the problem.
- If it says Unknown item 'modid:thing' (or block, fluid, biome or tag), the mod with that namespace is missing or a different version. Reinstall the version the pack expects, or find the data file that mentions modid:thing in config/, kubejs/, defaultconfigs/ or world/datapacks/ and move it out.
- If you removed a mod or swapped the pack on an existing world, put the old mod back, or start a new world. Mod content and world generation are stored with the world.
- If it names a file inside world/datapacks/, move that datapack out of the folder and check it was made for your Minecraft version.
- If it says You must set <key> ... server.properties, add that key with a value from the mod's own documentation.
- Restart, and repeat if a second cause appears. Packs that lose one mod often lose references in several places.
Tip
Since Java Edition 1.16 the server accepts --safeMode, which loads only the vanilla data pack. Use it as a test of whether data packs are at fault, not as the fix, and back up first: on a modded world it also leaves out the mods' own data.
What MineXHost's launcher does with this crash
MineXEngine, our launcher, stops the boot when this line appears before the server has finished starting, and reads the lines above it for the cause. A player typing the same words into chat on a running server does not trigger it.
When a data file references an item id that no installed mod provides, the engine renames that file so it is skipped (a rename, not a delete) and restarts. If the reference is not in a loose file but inside a mod's jar or a datapack zip, the engine can rewrite that archive without the one broken data entry. That does change the jar, so keep your own copy of the pack if you want the original.
It does not wipe your world over a datapack error on your server. A datapack it can name is moved to a holding folder, .mx-disabled-datapacks, where you can get it back; if it cannot tell which datapack is broken, it leaves them all in place and reports the problem. When a mod needs a server.properties setting, the log names the setting and the value is left to you. The engine never starts the server in safe mode.
Not every pack boots on a server. Our test results page shows how many public modpacks pass on each MineXEngine version, and how they were tested.
See the modpack test resultsMineXHost runs Forge, NeoForge and Fabric packs on MineXEngine. Our launcher detects the modpack, picks the right Minecraft loader and Java version, tunes the JVM for your RAM, and auto-recovers from the crashes that normally end a modded server's evening. Pick your RAM, paste the pack, and play.
See hosting plansFrequently asked questions
What does “Failed to load datapacks, can't proceed with server load” mean?
Failed to load datapacks, can't proceed with server load means the Minecraft server tried to load its data packs, which on a modded server includes every mod's own data, and one file failed to parse or referenced something that does not exist, so the server stopped before opening the world. The line just above it in latest.log names the actual file or id.
Do I have to delete my world to fix “Failed to load datapacks”?
Deleting the world is usually unnecessary, because this error is most often caused by a recipe, quest or other data file pointing at an item from a mod that was removed or changed, and putting that mod back or moving the one bad file out fixes it. Treat a new world as the last resort, after a backup.
Is --safeMode a fix for this error?
The --safeMode option, added to Java Edition in 1.16, starts the server with only the vanilla data pack, which tells you whether a data pack is at fault but leaves out the mods' own data on a modded server, so treat it as a diagnostic rather than a fix. Take a backup first, and fix the file the log names.
Why did “Failed to load datapacks” start after I removed a mod?
Removing one mod can leave a recipe, quest or loot table pointing at an item id that no longer exists, because the mods, quest books and scripts in a modpack reference each other's items, and the server treats a missing id as fatal while it loads data. Reinstall the mod, or remove the data file that references it.