Failed to load datapacks, can't proceed with server load: how to fix it

What "Failed to load datapacks" means on a Minecraft server

"Failed to load datapacks" means the server could not build the game data this world needs, so it refused to start it. Before a world loads, the server collects every data pack the world was saved with, adds the ones built into the game, the server software and your mods, and then reads the world's own generation settings: its seed and its dimensions. If one of those steps fails, you get this line and the server shuts down.

[ServerMain/WARN]: Missing data pack file/Terralith_1.21.11_v2.6.0.zip
[ServerMain/WARN]: Failed to load datapacks, can't proceed with server load. You can either fix your datapacks or reset to vanilla with --safeMode
java.util.concurrent.ExecutionException: java.lang.IllegalStateException: Overworld settings missing

The line itself never says what went wrong. Look at two places instead. Directly under it is the exception, which names the real problem. A little higher up, often only a few lines, the server lists every data pack it expected and could not find. Together they point to one of the causes below.

Read the "Missing data pack" lines first

A Missing data pack line means the world was saved with that pack switched on, and the server cannot find it now. On its own it is only a warning: plenty of servers start with one or two of them. It turns into a crash when the missing pack added something the world still uses, such as biomes or a whole dimension. The name after the words tells you where the pack used to come from.

Seeing Missing data pack paper on a Fabric, Forge or NeoForge server is common and harmless by itself. It tells you something useful, though: the world was last started on Paper, so it may also have been saved by a different Minecraft version.

Packs that only add recipes, loot or functions can go missing without any crash. The ones that matter here change world generation: Terralith, Tectonic, Incendium, Nullscape, mods that add dimensions, and anything that came with a modpack's own world. If you are not sure which pack shaped your terrain, the datapacks guide explains what a pack can change.

Overworld settings missing: a terrain datapack or mod is gone

Overworld settings missing means the server could not read how the Overworld is generated, because those settings refer to biomes or terrain rules that no longer exist. When a world is created with a terrain pack such as Terralith, the pack's biomes are written into the world's generation settings. In a Terralith world those settings name its biomes hundreds of times, every one as terralith:.... Take the pack away and the server reads a list full of names it has never heard of, throws the whole Overworld entry out, and stops.

1. 1

   Find the exact name

   Copy the name from the Missing data pack line. For file/Terralith_1.21.11_v2.6.0.zip that is the pack Terralith, version 2.6.0, made for Minecraft 1.21.11.

2. 2

   Get the same pack again

   Download the same pack, for the same Minecraft version, from the place you got it the first time. The same version is the safest choice: a newer release of a terrain pack can rename or drop biomes your world already uses.

3. 3

   Put it back where it was

   Stop the server. For a file/ pack, open the Files tab, go to world/datapacks and upload the zip as it is, without unpacking it. On Paper and Purpur this is the folder of the main world, not world_nether or world_the_end. For a mod: pack, put the mod back in mods.

4. 4

   Start and check the console

   Start the server. The Missing data pack line for that pack should be gone, or, if the file name changed, replaced by Found new data pack ..., loading it automatically. When the console reaches Done, the world is back.

On modded servers the same error shows up when a modpack update leaves out a mod that added biomes. Forge then writes Missing data pack mod:<modid> for every mod that is gone. Install those mods again, in the version the world was made with, or go back to the earlier pack version until you have a plan for the terrain.

Can I remove a terrain pack from an existing world?

Not by deleting the file. The world's generation settings keep pointing at the pack's biomes, so the server keeps refusing to start. If you really want to be rid of it, you have two honest options: start a new world without the pack, or change the world's generation settings back to vanilla with an NBT editor, which only changes how new chunks are generated. Land that was already generated keeps its blocks, although chunks that still name a missing biome are read as plains; the console says Unknown biome, defaulting to plains when that happens. Take a backup before you try the second one; our team can help customers with it.

Failed to get element ResourceKey: a custom dimension is gone

Missing data pack file/<pack>.zip
Failed to load datapacks, can't proceed with server load. You can either fix your datapacks or reset to vanilla with --safeMode
java.util.concurrent.ExecutionException: java.lang.IllegalStateException: Failed to get element ResourceKey[minecraft:worldgen/noise_settings / <namespace>:<name>]

This variant names the exact thing the server is looking for. noise_settings is the recipe for a dimension's terrain, and the part after the slash says which pack it belonged to: the namespace before the colon is usually the pack's or mod's short name. A world that once had a sky dimension, an extra Nether or a dungeon dimension from a pack keeps a reference to it, even when nobody has visited it in weeks.

The fix is the same as above: put the pack or mod that owns that namespace back, the same version as before. Paper and Purpur keep a separate level.dat in world, world_nether and world_the_end, and a custom dimension can be listed in all three. If you plan to remove such a dimension for good, that is a careful edit in more than one file, so keep a backup and ask our team when in doubt. Resetting the Nether or the End is a different job and does not remove a dimension's settings.

No key dimensions in MapLike, no key seed: a world from a newer version

No key dimensions in MapLike[{}]; No key seed in MapLike[{}] almost always means the world was saved by Minecraft 26.1 or newer, and the server now runs 1.21 or older. Starting with 26.1, the world's seed and dimensions are stored in their own file instead of inside level.dat. An older server opens level.dat, looks for the seed and the dimensions where it expects them, finds an empty spot, and stops. The {} in the message is that empty spot.

This typically happens after a version switch. A server starts on the latest release, the world is generated, and later the version is set back to 1.21.1 or 1.20.1 because a modpack or a plugin needs it. Uploading a world from a newer single player game to an older server ends the same way.

• Go back to the version that saved the world. In Settings, card Server software, choose that Minecraft version again (or a newer one), save and restart. The world loads as it was.
• Need the older version for mods or plugins? Then that world cannot come along. Restore a backup from before the world was opened on the newer version, or start a fresh world on the older version.
• Do not try to make it fit by hand. Minecraft does not support loading a world in an older version. Even when you get it to start, blocks and items from the newer release can disappear.

Ask the Copilot in our panel how to change the version and it gives the same advice: make a backup first, because going up is usually safe and going back down can damage a world that a newer version already opened. When you pick an older version in Settings, the panel also checks which version saved your world first. If the world is newer, it stops and says so, and you choose between keeping a version that can open the world and starting a fresh world while the old one is kept aside. Moving a server to a new host has the same rule for worlds you bring along.

Unable to read or access the world gen settings file (Minecraft 26.1 and newer)

[Worker-Main-1/ERROR]: Unable to read or access the world gen settings file! Falling back to the default settings with a random world seed. ./world/data/minecraft/world_gen_settings.dat
[main/WARN]: Failed to load datapacks, can't proceed with server load. You can either fix your datapacks or reset to vanilla with --safeMode
java.util.concurrent.ExecutionException: java.lang.IllegalStateException: Overworld settings missing

On Minecraft 26.1 and newer, the seed and the dimensions live in world_gen_settings.dat, and this line means the server could not read that file. It names the path it tried, and the path differs per server software: vanilla, Fabric and NeoForge look in world/data/minecraft/, while Paper looks in world/dimensions/minecraft/overworld/data/minecraft/. Despite the friendly sound of "falling back to the default settings", the start still fails a moment later with Overworld settings missing.

• The world came from other server software. A Missing data pack paper line on a Fabric, NeoForge or vanilla server means Paper saved this world last. Switch back to the software and version the world was saved with, and it starts again.
• A mod's generator is gone. When the line continues with Unknown registry key and a name such as bclib:betterx, a mod that generated this world's terrain is missing. Install it again.
• The file is not there at all. Check the folder from the error on the Files tab. An uploaded world without its data folder is incomplete; upload the whole world folder again.

Failed to load registries due to above errors: a pack that does not fit

Failed to load registries due to above errors means a pack was found but its contents could not be read. The useful lines are the ones above it, as the message says: scroll up past the stack trace and look for the first ERROR that names a file inside a pack, usually a .json file somewhere under data/<namespace>/. A common reason is that the pack was made for another Minecraft version, where that file had a different format.

Get the release of the pack that matches your server's Minecraft version and replace the old file. If the pack has no release for your version, take it out of world/datapacks only when it does not change terrain; for terrain packs, the world needs it, so stay on the version the pack supports. The guide to crash reports and logs shows how to scroll through a long trace without getting lost.

Does --safeMode fix it?

--safeMode rarely fixes this error on a real server. It starts the server with only the vanilla data pack, which helps when one broken pack stops everything and the world itself does not depend on it. In the cases above, the world does depend on what is missing: its settings still name the biomes, the dimension or the newer file layout, with or without your other packs. Safe mode cannot invent those.

It is also a start option of the server program, not a setting in server.properties, so it has to be added to the start command. On our plans you will not need it: putting the missing pack back, or choosing the right version, gets you further every time.