Sometimes your collection may become very damaged. For instance:
- You accidentally deleted a card type or hundreds of cards and didn't notice in time to undo it.
- Your collection has become corrupted.
- There was a syncing error and you accidentally overwrote a large number of reviews that you did on another device.
- ...or anything else that leaves you with lost data.
Anki automatically backs up your collection every time you close Anki or sync (AnkiMobile backs up after fixed time intervals and before syncs), and by default it stores 30 backups. For information on restoring an automatic backup, please visit the relevant page: