How does it decide two files are the same?

Files are grouped by size first, since two files of different sizes cannot possibly be identical. Anything left is hashed with SHA-256 and grouped by the result. Two files with the same SHA-256 are the same file — the odds of a coincidence are not something you will ever encounter.

Will it find similar photos, or two versions of the same song?

No. This finds byte-identical files only. A photo that has been resized or re-saved is a different file, even if it looks the same to you — finding those needs perceptual comparison, which is a different tool entirely.

Can I select a whole folder?

In most desktop browsers you can open the file picker, select a folder's contents with Ctrl+A or Cmd+A, and add them all at once. The total is capped at 500MB because everything is held in the tab's memory.

Duplicate File Finder

Select a folder's worth of files and this finds the ones that are genuinely identical. It compares contents rather than names, so "invoice.pdf" and "invoice (1) final COPY.pdf" are caught if they are the same file, and two different photos that happen to share a name are not. Files with a unique size are ruled out without being read at all, so a large folder is quicker to check than you would expect.

Drop a folder's worth of filesor click to browse — select as many as you like, they are compared on your device

Nothing is uploaded — this tool runs inside your browser, so your files never leave your device.

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Why use this tool

Compares file contents, so renamed copies are still caught
Groups every duplicate set and shows how much space they waste
Rules out unique file sizes without reading them, so it's fast
Runs in your browser — nothing is uploaded and nothing is deleted

How it works

1Select the files you want to compare — as many as you like.
2Press Find duplicates.
3Delete the copies yourself, keeping the one marked keep.

Duplicate File Finder — frequently asked questions

No, and it can't. A web page has no access to your filesystem beyond the files you hand it, so it can only report what it found. You delete the copies yourself, which is the right way round for an operation nobody wants done automatically.

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