Recovering Corrupted Minecraft Worlds

1. Symptoms of World Corruption

World corruption typically surfaces after improper power halts or faulty entity mods. In your console, look for errors like:

net.minecraft.ReportedException: Loading NBT data
java.util.zip.ZipException: Not in GZIP format
java.lang.ArrayIndexOutOfBoundsException: Index 4096 out of bounds for length 4096

2. Identifying the Bad Region Coordinates from Crash Logs

Examine crash-reports/crash-YYYY-MM-DD.txt. Scroll down to the Chunk Stats section to find the corrupted region file (e.g. r.2.-1.mca).

3. Repairing Chunks with RegionFixer

Download the free Python tool Minecraft-Region-Fixer on your PC:

# Scan your world folder for bad chunks:
python region-fixer.py /path/to/world

# Replace corrupted chunks with clean empty chunks:
python region-fixer.py --replace-corrupted /path/to/world

4. Recovering from level.dat_old

If your server crashes saying level.dat is corrupted, Minecraft maintains an automatic backup:

1. In your world directory, delete the corrupted level.dat.
2. Locate level.dat_old and rename it to level.dat.
3. Start your server. The world headers will re-initialize cleanly.