If you’ve ever browsed a Kindle’s documents folder through a file explorer, you’ve seen them: .sdr folders scattered everywhere, one for nearly every ebook that has ever passed through the device. Each ebook on a Kindle generates a companion folder storing bookmarks, reading position, annotations, and notes. When you delete a book through the Kindle’s interface, the SDR folder goes with it. But when you delete books via USB, manage your library through Calibre, or restore from backups, those SDR folders often stay behind. Over months or years, these orphans accumulate into hundreds — sometimes thousands — of useless files cluttering your Kindle’s storage. SDR-Cleaner is a free, lightweight tool that finds and removes orphaned SDR folders automatically. It takes about five seconds to run and never touches books you still have on the device.
What SDR folders actually are
Every ebook you open on a Kindle creates a folder named after the book’s ASIN (Amazon Standard Identification Number) or filename, ending in .sdr. Inside are several tiny files that track your interaction with the book:
- Reading position — the exact page or location where you stopped reading, so Whispersync and the Kindle itself can resume correctly.
- Bookmarks — any pages you’ve manually bookmarked for later reference.
- Highlights and annotations — every passage you’ve highlighted and every note you’ve typed.
- Last page read metadata — timestamp and location data used by the Kindle’s “Time to read” estimates and reading statistics.
These folders are essential while the book lives on your Kindle. They’re what make the reading experience feel seamless — you close a book, open it days later, and you’re right where you left off, with all your highlights intact.
The problem is that SDR folders aren’t always cleaned up when books are removed. Deleting a book directly from the Kindle’s home screen (long-press, “Remove from Device”) does remove the SDR folder. But if you delete books by connecting the Kindle to a computer and deleting files through the file system, or if you use Calibre to send and remove books in bulk, the SDR folders for removed books remain. The Kindle itself doesn’t run a cleanup process to find and remove orphaned SDR folders — they just sit there indefinitely.
Why SDR buildup matters
A single orphaned SDR folder is negligible — usually only a few kilobytes. But multiply that by hundreds or thousands of books over the life of a Kindle, and the cumulative effect becomes noticeable. On a Kindle with limited storage (many models have only 8 GB, with about 6 GB usable), several hundred orphaned SDR folders can consume tens of megabytes of space. More importantly, they make the documents folder a mess. If you ever need to manually browse your Kindle’s file system to find a specific book file, you’re wading through hundreds of extra folders. For users who sideload a lot of content and rotate their library frequently, this clutter grows fast.
What SDR-Cleaner does
SDR-Cleaner solves this with a straightforward comparison approach. It scans your Kindle’s documents folder and builds a list of every .sdr folder it finds. Then it checks each one against your actual ebook files — MOBI, AZW3, KFX, and PDF files. If an SDR folder has a matching book file still present on the device, it stays untouched. If there’s no matching book anywhere on the Kindle, the SDR folder is flagged as orphaned and can be deleted.
This comparison-based safety check is what makes SDR-Cleaner trustworthy. It never deletes anything associated with a book you still have. Your reading progress, highlights, and bookmarks for active books are always preserved. The only folders removed are the ones that have no corresponding book on the device — the digital equivalent of bookmarks left in books you’ve already donated.
SDR-Cleaner is available as a free download:
macOS / Linux
brew install gamepunk/ink-cli/ink
ink cleanWindows
# Download from https://github.com/zdavatz/sdrcleaner/releasesStep-by-step usage
Using SDR-Cleaner is intentionally simple. There’s no complex configuration and no risk of deleting the wrong thing. Here’s the full process:
- Connect your Kindle to your computer via USB. The Kindle should appear as a removable drive in your file explorer. On macOS it mounts on the desktop; on Windows it appears under “This PC” with a drive letter.
- Download SDR-Cleaner from the BookFere website or from the GitHub releases page. The tool is a single executable — no installation required.
- Launch SDR-Cleaner. On Windows, double-click the
.exefile. The tool auto-detects any connected Kindle drive, so you don’t need to navigate to the right folder manually. If you have multiple Kindles connected, it lists them and lets you choose. - Review the scan results. SDR-Cleaner displays a count of how many orphaned SDR folders it found before it deletes anything. This transparency lets you verify that the number makes sense — if it finds thousands when you expected dozens, something might be wrong.
- Click “Clean” and wait a few seconds. The tool deletes all orphaned folders in one pass.
- Safely eject your Kindle from your computer before unplugging the USB cable.
The entire process takes under a minute from plugging in to finishing. After cleaning, your Kindle’s storage has a little more breathing room and the file system is noticeably cleaner if you ever need to browse it manually.
When to run SDR-Cleaner
SDR-Cleaner isn’t something you need to run daily. It’s a maintenance tool for specific moments in your Kindle workflow.
After deleting a large batch of books. If you just removed 50 books from your Kindle — whether through the device itself or through Calibre — running SDR-Cleaner ensures none of their SDR folders got left behind. The Kindle’s built-in cleanup is reliable for individual deletions, but bulk operations sometimes miss folders.
Before a major library sync. If you’re about to sideload a large number of new books through Calibre or send-to-Kindle, clean up first. A tidy documents folder means fewer files for the Kindle to index, which speeds up the post-sync processing where the device builds its internal database of your library.
When the Kindle feels sluggish. A Kindle that’s slow to open books or navigate the home screen sometimes benefits from storage cleanup. While orphaned SDR folders alone don’t cause significant slowdowns, removing them as part of a broader cleanup (along with old firmware update files and leftover temp files) can help.
Every three to six months as routine maintenance. Even if you don’t notice any problems, a periodic cleanup keeps the Kindle’s file system healthy. Set a calendar reminder and run it alongside other digital housekeeping tasks.
Troubleshooting
SDR-Cleaner is reliable, but a few things can trip it up.
The Kindle isn’t detected. Make sure the Kindle is unlocked and on the home screen before connecting it. Some Kindle models won’t mount as a drive if they’re asleep or showing a book. Try a different USB cable — some cheap cables are charge-only and don’t support data transfer. On macOS, check that the Kindle drive appears in Finder; if not, try a different USB port.
SDR-Cleaner finds zero orphaned folders. This can happen if you always delete books from the Kindle’s own interface and never sideload. It’s also possible that a previous run already cleaned everything. Either way, zero orphans is good news — your Kindle is tidy.
SDR-Cleaner finds an unexpectedly high number. If the count seems impossibly high, don’t panic. The tool is counting individual SDR folders, and if you’ve used the same Kindle for years with heavy sideloading, hundreds of orphans are plausible. Review the list if the tool provides one, then proceed with cleaning.
Alternatives to SDR-Cleaner
If you prefer not to use a third-party tool, you can clean orphaned SDR folders manually by browsing your Kindle’s documents folder and comparing SDR folder names against your book files. This is tedious with more than a handful of books and error-prone — it’s easy to accidentally delete the wrong folder.
Calibre itself doesn’t clean orphaned SDR folders. Some users write shell scripts or batch files to automate the comparison, but that requires technical comfort and varies across operating systems. SDR-Cleaner remains the simplest option for most users.
Preventing SDR buildup
The single most effective prevention strategy is to always delete books directly from the Kindle’s interface rather than through USB or Calibre’s device view. Long-press a book cover, tap “Remove from Device,” and the Kindle handles both the book file and its SDR folder together.
When you do need to manage books through Calibre, run SDR-Cleaner afterward. Consider keeping fewer books on your Kindle at any one time — a smaller, curated library means fewer deletions and less SDR folder accumulation overall. I keep about 30-50 books on my Kindle at once, rotating new ones in and finished ones out. This library size is manageable, loads quickly, and minimizes the cleanup burden.
SDR-Cleaner is one of those tools you install once and forget about until you need it. It does one thing, does it safely, and costs nothing. For anyone who sideloads books onto a Kindle, it earns a permanent spot in the toolkit.