The following operations are for use only in rare, specific situations and should not be used for general troubleshooting. In many cases, resetting will cause additional problems. Before using any of these options, please ask for help on the Zotero forums.

By default, the Zotero sync process merges data between the Zotero desktop client and the Zotero server. In certain rare situations, Zotero's record of previous syncing may become corrupted, leading to sync errors or changes to items not being detected. These errors can be corrected by resetting your Zotero sync history, which force Zotero to check each of items or files for changes and sync them.

If the Zotero sync icon is spinning and you're trying to fix it, do not use the reset options. Instead, wait for the sync to finish or report the problem on the Zotero forums.

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

If changes made to an item are not being detected and synced on your computer, this option will reset the item data syncing history between your local Zotero database and the Zotero servers. This will merge your local data with the remote data on the Zotero servers, ignoring any existing sync history (i.e., the data in both locations will be merged).

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.

If you have made changes to your local Zotero database that you wish to undo, and these changes have not yet synced with the Zotero servers, see Restoring from Backup. Note that this is unlikely if you have automatic sync enabled and an active internet connection.

If your changes have already synced, you can restore your online library from a backup of your local library by following these steps:

1. First, make sure to keep Zotero running, as the automatic backup might be overwritten when you quit the application.
2. If you're using syncing, temporarily disable auto-sync in the Sync pane of the Zotero preferences.
3. Locate your Zotero library and make a copy of any zotero.sqlite.bak files. The timestamps of the files may help you determine which file would contain the data you're trying to restore.
4. Close Zotero. In your data directory, rename zotero.sqlite to zotero.sqlite.old, rename one of the .bak copies you made to zotero.sqlite, and restart Zotero. You should now see the backed-up version of your library.
5. Were you to sync again now, the more recent data in the online library would replace the data you just restored. 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.
6. 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.]

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