How to put your Calibre library in the cloud without corrupting it

Updated October 27, 2026 · 8 minute read

Putting a Calibre library in Dropbox, OneDrive or Google Drive is the most common way to damage it. Here is a setup that keeps the library safe on your computer and still makes it available everywhere.

Why sync folders corrupt Calibre libraries

Calibre keeps everything it knows about your books in one SQLite database, metadata.db, and writes to it constantly while it is open. Sync clients copy files while they are being written, and when two computers open the same library they overwrite each other’s changes. The result is the familiar “database disk image is malformed” error, or books that vanish from the list. Calibre’s own documentation advises keeping the library on a local disk.

The safe setup: one-way copy to a bucket

The library stays on your computer, where Calibre expects it. After you close Calibre, a copy tool mirrors it to cloud storage. Nothing ever writes back, so nothing can conflict. useCalibre then reads the copy.

1. Create a bucket

Any S3-compatible storage works. Cloudflare R2 is a good default: it has a free allowance of 10 GB and charges nothing for downloads, which suits a book library. Amazon S3, Backblaze B2 and Wasabi work just as well.

1. Create a private bucket, for example my-books.
2. Create two API keys: one with read and write access for your computer’s copy tool, and one with read-only access for useCalibre.

2. Copy the library with rclone

rclone is a free command-line tool for copying files to cloud storage. Install it, run rclone config and add your bucket as an S3 remote (choose your provider, for example Cloudflare, and paste the read-write key). Then, with Calibre closed:

rclone sync "C:\Users\you\Calibre Library" "r2:my-books/Calibre Library" --dry-run

Check what it would do, then run it again without --dry-run. sync makes the bucket match your library, so books you delete in Calibre disappear from the copy too. Always copy from the library to the bucket, never the other way.

3. Keep it up to date

• By hand: run the command after a Calibre session.
• On a schedule: Windows Task Scheduler, a macOS launchd job or a cron entry, at a time Calibre is usually closed, such as overnight.

useCalibre checks for a new metadata.db every few minutes and imports the changes on its own.

4. Connect it to useCalibre

1. Create a free account at app.usecalibre.com.
2. Under Manage → Connect a Calibre library, enter the bucket, the folder (Calibre Library) and the read-only key.
3. useCalibre checks metadata.db for damage, imports your catalog and caches the covers. Start reading.

What if my library is already in Dropbox or Google Drive?

Move it to a folder outside the sync folder (in Calibre: the library button, then Switch/create library, then move), run Library maintenance → Check library, and then follow the steps above.