A BAK3 file is a backup file used by Starbound, an open, sandbox 2D space exploration game. It stores backup information for the game, which may be about a spaceship or player character. BAK3 files are helpful for recovering information in the event of a computer crash or corrupt SHIPWORLD or PLAYER file.

BAK3 files are named with the ".bak3" extension added to a PLAYER or SHIPWORLD file. For example, if the file is storing backup information for a SHIPWORLD file, the filename would be ab 07704dbcb4162646d4d93bbeef34df.shipworld.bak3. You can delete the ".bak3" extension from the filename and open the file as a SHIPWORLD file in Starbound. However, it is important that you do not change the string of characters preceding the extensions. BAK3 files can be found in the "player" folder in the "Starbound" folder. For example if you purchased Starbound through Steam, the BAK3 files are stored in the following location in Windows: C:/Program Files/Steam/SteamApps/common/Starbound/player NOTE: Starbound also uses .BAK1 and .BAK2 files.