Help & User Guide

Quick Start

1. Add folders — click the + button or drag folders onto the Dopp window. You can add as many folders as you like, including folders from different locations.
2. Scan — click the Scan button. Dopp reads every file in every folder you added and groups identical files together.
3. Review the results — each group shows the copies side by side. Mark each file as Keep or Trash.
4. Send to Trash — once you have reviewed the groups you want to act on, click Send to Trash. Files go to the macOS Trash, not permanent deletion.

How Dopp Finds Duplicates

Dopp uses SHA-256 content hashing. It reads the actual bytes of each file and produces a unique fingerprint. Two files are considered duplicates only if their fingerprints match exactly — meaning their contents are byte-for-byte identical.

This means Dopp will catch duplicates even when:

• The files have different names
• The files are in different folders
• The files have different modification dates
• One is a copy created by drag-and-drop or a backup tool

Dopp also uses a size pre-filter: it skips files that can't possibly be duplicates (because no other file has the same size) before doing any hashing. This makes scanning fast even on large collections.

Reviewing Duplicate Groups

Each group in the results list represents a set of files with identical content. For every file in a group you can see:

• The full path to the file on disk
• The file size
• The last modification date

Click any file (or press Space, just like in Finder) to open a Quick Look preview. This is especially useful for images and PDFs where you want to confirm which copy is the one you want to keep.

For each file, choose one of three states:

• Keep — this copy will not be touched
• Trash — this copy will be sent to the Trash when you confirm
• Undecided — default state; this file is not processed until you decide

You can reset an individual group back to undecided at any time by clicking the reset button on that group.

Sorting & Filtering

Use the sort control to prioritise which duplicate groups to review first:

• Most space wasted — groups where the most disk space can be reclaimed appear first. Best starting point when storage is your primary concern.
• Largest file — groups containing the biggest individual files appear first.
• Most copies — groups with the most duplicate copies appear first.

Use the filter control to show only:

• All groups — every duplicate group found
• Undecided only — groups where you haven't yet made a Keep/Trash decision
• Ready to process — groups where at least one file is marked Trash and at least one is marked Keep

Bulk Decisions

Instead of reviewing every group manually, you can use bulk actions to pre-fill decisions across all groups at once. Find these in the toolbar:

• Keep First, Trash Rest — marks the copy found in the first folder you added as Keep; all other copies are marked Trash. This is ideal when you have a "master" folder that should always win.
• Keep Newest — in each group, keeps the file with the most recent modification date and marks the rest as Trash.
• Keep Oldest — in each group, keeps the file with the earliest modification date. Useful when the oldest copy is your original.
• Clear All Decisions — resets every group back to undecided so you can start the review from scratch.

After using a bulk action, review the results before sending to Trash — bulk decisions are a starting point, not a guarantee. You can override any individual decision after applying a bulk action.

Safety & Undo

Files are moved to the Trash, not permanently deleted. When you click Send to Trash, the files go to your macOS Trash and remain there until you empty it. If you change your mind, simply open the Trash and move them back.

Dopp's built-in Undo can reverse the most recent Send to Trash operation in one click — it moves every file from that batch back to its original location, even if the Trash hasn't been emptied yet. This is faster than manually restoring files from the Trash one by one.

Dopp only has access to the folders you explicitly added to the scan. It cannot read or modify anything outside those folders.

Tips & Tricks

• Add your most trusted folder first. The "Keep First" bulk action keeps files from the first-added folder. If you have a "master" photos library, add it before your backup or downloads folder.
• Use Quick Look before deciding. For images, especially photos that were saved at different times, press Space on each file in a group to confirm they really are identical before trashing any.
• Filter to "Ready to Process" before sending. This lets you review only the groups you've already decided on before committing — a good final check.
• Don't empty the Trash right away. After a large scan, leave the files in the Trash for a day. Make sure nothing is missing before permanently deleting.

Frequently Asked Questions

Troubleshooting