Compare Two Folders

About the folder comparison tool

"Did the backup actually copy everything?" is a question that is surprisingly hard to answer. Both folders look the same in the file manager, the sizes are roughly similar, and the only way to be sure is to check file by file. This tool does that check: pick two folders and it tells you what is in one and not the other, and what exists in both but is no longer the same.

Files are paired by their path relative to each folder you picked, so comparing D:\Projects\site with E:\Backup\site pairs css/app.css with css/app.css no matter how different the two absolute paths are.

Both folders are read inside your browser. Nothing is uploaded, both are opened read-only, and neither is modified.

How to use it

• Choose folder A, then choose folder B. The comparison runs as soon as both are loaded
• Pick how to compare — size only, size and date, or the actual file contents
• Read the four groups — in B only, missing from B, changed, identical
• Copy the report or download it as a CSV

The four results

• In B only — files that exist in B but not in A. New work, or files added since the copy was made
• Missing from B — files in A that never made it to B. This is the one that matters for a backup: anything listed here was not copied
• Changed — the same path exists in both, but the file is no longer the same. The report shows both sizes and dates side by side, and says which check flagged it
• Identical — same path, same file. Counted always, listed only if you tick the box, because on a real folder this is usually the longest list by far

Choosing how to compare

This is the setting that decides how much you can trust the answer.

• Size only — fastest, and reads nothing. Two files of different lengths are certainly different, so this catches most real edits instantly. It cannot catch a change that happens to preserve the file size
• Size and date — also flags files whose modification time differs. Useful, but noisy: copying files often resets timestamps, so a perfect copy can show up as "changed" everywhere
• File contents — computes a SHA-256 hash of both copies and compares them. This is the only answer that is certain, and the only one that will tell you a file is genuinely identical despite a different timestamp. It reads every byte of both folders, so it is much slower

A useful habit: run size only first to see the shape of the difference, then switch to file contents when you need to be sure.

The other options

• Include subfolders — off compares only the files sitting directly in each folder; on compares the whole tree
• Ignore upper/lower case in names — Windows treats Photo.JPG and photo.jpg as the same file, macOS and Linux usually do not. Tick this when comparing a Windows folder against a copy made on another system, or the same file will appear as both added and missing
• List identical files too — include the full identical list in the report and the CSV

What people use it for

• Confirming a backup really copied everything before wiping the original
• Finding what changed between a project folder and a copy taken last week
• Checking whether a file sync actually finished
• Comparing two versions of a website or app folder before deploying
• Working out what a colleague changed in a shared folder they sent back
• Verifying files after moving them between drives or restoring from an old disk

Two ways your browser reads a folder

Chrome, Edge and Opera support a proper folder picker, which is the route this tool is built for: each folder is walked directly, and content comparison reads the bytes through the folder handle.

Firefox and Safari use the older folder upload control. The browser hands over every file in each tree at once, so comparison works the same way, but an empty folder cannot be seen — no file inside it reveals it exists — and both trees are loaded in full before anything is compared.

Good to know

• Nothing is uploaded. Both folders stay on your machine and every comparison happens in the page
• Both folders are opened read-only. Nothing is created, renamed, moved or deleted in either one
• A file that cannot be read — locked, in use, or in a protected system folder — is reported as changed with the reason, rather than being silently dropped
• Content comparison reads both copies of every same-size file, so on large media folders it takes a while. The progress bar shows how far along it is
• Each folder is capped at 200,000 items so the page cannot freeze
• The CSV includes a byte-order mark so accented and non-Latin filenames open correctly in Excel

Related tools

• Folder & File List — list everything in a single folder
• Duplicate File Finder — find identical files inside one folder
• Bulk File Rename — rename a whole folder at once
• Text Diff — compare the contents of two pieces of text