How to Fix Advancement Loading Crash
Broken advancement files are logged and skipped instead of crashing the game. How to find the file, fix it and keep player progress safe.
Quick Fix
Search latest.log for Couldn't parse data file or Couldn't parse player advancements, then fix the data pack file or restore the player's progress file from a backup.
Error Message
Couldn't parse data file 'mypack:my_advancement' from 'mypack:advancement/my_advancement.json'How to Fix
Search latest.log for the advancement id and open the file it names.
Fix the JSON or compare it with a vanilla advancement, then run /reload.
Move files from data/<namespace>/advancements to data/<namespace>/advancement for 1.21 and later.
Copy a damaged progress file somewhere safe right away. The game writes the player's current progress over it the next time it saves that player, for example when they log out.
Restore the player's file from a backup while the server is stopped. It is named after the player's UUID and lives in players/advancements since 26.1, and in advancements before that.
Delete a player's progress file only as a last resort, because the player loses all advancement progress.
Common Causes
- A data pack advancement isn't valid JSON or doesn't match the format. The game logs Couldn't parse data file with the advancement id and skips it.
- An advancement loads but the game finds problems in it. The log lists them under Found validation problems in advancement, followed by its id.
- A player's progress file is damaged. The log shows Couldn't parse player advancements in, followed by the file, and that player starts without advancement progress.
- The data pack still uses the old advancements folder. Since 1.21 the folder is data/<namespace>/advancement.
- Progress refers to advancements that no longer exist, for example after removing a data pack. The game ignores those entries and keeps the rest.
Diagnostic Steps
- Search latest.log for advancement errors.
- Fix or remove the file in the data pack.
- Copy damaged progress files and restore them from a backup.
- Run /reload or restart and check the log.
FAQ
Will clearing advancements affect gameplay?
The player loses advancement progress but keeps items, experience and the world. Advancements can be earned again.
Where is advancement progress stored?
In one JSON file per player, named after the player's UUID: in players/advancements inside the world folder since 26.1, and in advancements before that.
Does a broken advancement crash the game?
Not in vanilla. The broken file is logged and skipped, and every other advancement still loads.
