Duplicate Detection

Grimmory can scan a library for duplicate books and merge them together. When duplicates are found, you choose which book to keep as the target and the other books’ files get attached to it as alternative formats. This is useful when you have the same book in multiple formats (EPUB and PDF, for example) or accidentally imported it twice.

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Opening the Duplicate Finder

Right-click (or click the three-dot icon) on any library in the sidebar or library header, then select Find Duplicates.

This opens the Find Duplicates dialog, scoped to that library.

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Detection Modes

Before scanning, choose how aggressively Grimmory should look for duplicates. Four presets are available, or you can configure individual signals manually.

Presets

Preset	Matches By	Best For
Strict	ISBN, External ID	High-confidence matches only
Balanced	ISBN, External ID, Title + Author	General use (default)
Aggressive	All 5 signals	Catching every possible duplicate
Custom	Your choice	Fine-tuned control

Detection Signals

Expand the Advanced section to see and toggle individual detection signals:

Signal	How It Works
ISBN	Matches books sharing the same ISBN-13. Automatically converts ISBN-10 to ISBN-13 for comparison.
External ID	Matches books that share an identifier from Goodreads, Hardcover, Google Books, ASIN, Audible, or ComicVine. Uses a union-find algorithm, so if Book A and Book B share a Goodreads ID, and Book B and Book C share an Audible ID, all three are grouped together.
Title + Author	Matches books with the same normalized title whose authors overlap. Title normalization strips whitespace and casing differences. Author comparison checks for name overlap between the two books.
Same Directory	Matches books whose files live in the same directory within the library.
Filename	Matches books whose filenames are similar after normalization (lowercased, underscores/hyphens replaced with spaces, special characters removed).

Start with Balanced

The Balanced preset is a good starting point. It catches most real duplicates without too many false positives. Switch to Aggressive if you suspect there are more, or Strict if you only want certain matches.

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Scanning for Duplicates

Click Scan to run the detection. Grimmory checks every book in the library against the enabled signals and groups duplicates together.

Results appear as numbered groups. Each group contains two or more books that Grimmory believes are duplicates, along with a colored badge showing why they matched:

Badge	Meaning
ISBN	Shared ISBN
External ID Match	Shared identifier from a metadata provider
Title + Author	Same title with overlapping authors
Directory	Files in the same folder
Filename	Similar filenames

Each book in a group shows its cover, title, author(s), and format badge (EPUB, PDF, AZW3, etc.).

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Selecting a Target

Every group has one book pre-selected as the target, indicated by the TARGET label and a highlighted row. The target is the book you want to keep. All other books in the group are “source” books whose files will be attached to the target.

Grimmory picks the suggested target automatically based on:

1. Format priority (EPUB is preferred over PDF, etc.)
2. Number of files (more files = higher priority)
3. Metadata completeness

You can change the target by clicking the radio button next to any other book in the group.

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Merging Duplicates

Merging a Single Group

Click Merge on a group to merge the source books into the target. What happens:

1. Source books’ files are moved into the target book’s directory
2. The files become alternative formats on the target book
3. If Delete source books is checked, the source book entries are removed from your library

Merging All Groups

Click Merge All at the top right to process every group at once. A progress indicator shows how many groups have been processed. After completion, a summary shows how many merges succeeded or failed.

Dismissing a Group

Click Dismiss on any group to skip it. The group is hidden from the results but no changes are made. This is useful when Grimmory flags books that aren’t actually duplicates.

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Delete Source Books

The Delete source books checkbox (enabled by default) controls what happens to source books after a merge:

Setting	Behavior
Checked	Source books are deleted from the library after their files are attached to the target
Unchecked	Source books remain in the library but lose their file associations

Files Are Moved, Not Copied

During a merge, source book files are physically moved to the target book’s directory. The source books’ original directories are cleaned up if empty.

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Notes

• Duplicate detection is scoped to a single library. It does not compare books across different libraries.
• Folder-based audiobooks cannot be merged because their directory structure is integral to playback.
• File naming follows the library’s configured naming pattern. If a filename conflict occurs, Grimmory appends a numeric suffix (e.g., _1, _2).
• File monitoring is temporarily paused during the merge to prevent the scanner from reacting to file moves.
• Merging is not reversible. If you’re unsure about a group, use Dismiss to skip it.

Back Up First

If you have a large number of duplicates, consider backing up your library folder before running a bulk merge.