The following operations are for use only in rare, specific situations and are not necessary during normal usage or for general troubleshooting. In many cases, resetting will cause additional problems. If you're not sure what these options do, please ask for help on the Zotero Forums before using them.

Before using any options on this page, make sure to first back up your Zotero library.

If you've made changes to a Zotero library locally and these changes have already synced to the online library, you can restore the online library from a backup of your local library by following these steps:

1. Temporarily disable auto-sync in the Sync pane of the Zotero preferences.
2. Without closing Zotero, make a backup of all zotero.sqlite files in your Zotero data directory.
3. Restore your database from either an external backup you've made or one of the automatic backups in your Zotero data directory. See Restoring Your Zotero Library from a Backup for more details.
4. You should now see your data as you want to keep it in Zotero. Were you to sync again now, the more recent data in the online library would replace the data you just restored.
   1. If you're trying to restore a small number of deleted items or notes, you can simply duplicate the items — by right-clicking and choosing “Duplicate Item(s)” — so that the new copies remain even after syncing.
   2. If many items were affected or collections were deleted, you can use Restore to Online Library from the Sync → Reset pane of the Zotero preferences to force Zotero to upload the local version of the library, overwriting previously synced changes. [Note: This functionality will be available in Zotero 5.0.31. Until then, install the 5.0 Beta, perform the restore, and switch back to the main version.]

If you're happy with the results, you can re-enable auto-sync and continue working. Keep any backups you created until you're sure all your data is intact.

If changes made to attachment files are not being synced (e.g., edits, annotations, deleting an attachment, adding a new attachment), this option will reset the file syncing history between your local Zotero database and your storage service (either the Zotero servers or your WebDAV provider). This will cause Zotero to compare all attachment files on your local computer with the ones on your storage service, making the most recent changes to files.

Resetting file sync history should not be necessary, so if you find that files aren't syncing correctly, see Files Not Syncing for help troubleshooting and reporting the issue.