Renaming a folder full of files at once
Renaming dozens or hundreds of files at once splits into a few options, and none of them are quite right. Select a batch in File Explorer and press F2, and you get "name (1)", "name (2)" in sequence — you don't get to say what the name should actually be.
The existing tools each fail somewhere different. Bulk Rename Utility packs its whole interface into one dense screen that reviewers regularly compare to a cockpit. PowerRename needs you to understand regex capture groups (^, $) to get the result you actually want. Advanced Renamer is free for personal use but $45 for commercial use. And all three need installing — plenty of office machines block installs outright.
The order of the rules is the whole point
Find-and-replace, numbering, and a prefix or suffix apply in that order, and the order carries meaning. Add a "photo_" prefix and turn on numbers-only, and you get photo_01, photo_02. Turn numbering off and use only find-and-replace, and it swaps that one string inside each existing name while leaving the rest alone. Set the digit count to 2 and numbering starts at 01; set it to 3 and it starts at 001.
Clashes get caught before anything runs
If a rule sends two files to the same result name, whichever renames second overwrites the first. So the preview computes every result name before touching anything, and if even one clash turns up, the run button stays off until it's resolved. Adjust the rule, watch the clash disappear, then run it.
A rename is a label change, not a copy
Renaming a file on disk doesn't rewrite its contents — it relabels it. That's why a multi-gigabyte video renames instantly and not a single byte of it gets rewritten. Undo works the same way, and just as fast, but it runs the steps in reverse: a name freed up earlier in the batch can get claimed again by a file further down, so undoing in forward order can recreate the exact clash you just avoided.
Chrome and Edge only
Opening a whole folder and editing the files inside it directly is a Chromium feature — Firefox and Safari don't have it yet, so this tool just shows a notice instead of doing anything on those browsers. The page also needs to be loaded over https to open a folder at all. Files are read and written only inside the folder you pick, and nothing leaves your computer.