Minecraft 26.x world upgrade doctor
Java Edition 26.1 moved almost every folder inside a world. Drop yours and this says which layout it has, exactly which paths the upgrade will move, and, if it has already run, whether anything was left behind in the old places.
The upgrade is one way. A converted world cannot be opened by an older release, so the copy you take before starting the new server is the only way back. Nothing here is uploaded: only file and folder names are read, in your browser.
The folder named after your world, the one holding level.dat.
On a server that is usually world/.
What 26.1 moved
| Before | After 26.1 |
|---|---|
region/ | dimensions/minecraft/overworld/region/ |
DIM-1/ | dimensions/minecraft/the_nether/ |
DIM1/ | dimensions/minecraft/the_end/ |
playerdata/ | players/data/ |
advancements/ | players/advancements/ |
stats/ | players/stats/ |
data/scoreboard.dat | data/minecraft/scoreboard.dat |
data/map_1.dat | data/minecraft/maps/1.dat |
data/idcounts.dat | data/minecraft/maps/last_id.dat |
resources.zip | resourcepacks/resources.zip |
26.1 also requires Java 25 and raised the default allocation from 2 GB to 4 GB. A server started on Java 21 refuses to boot rather than degrading, which is a separate failure from anything to do with the world; the log analyzer names it from the log line.
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