RunToolRunBulk File Rename
Rename multiple files in bulk.
How to Rename Files in Bulk
Select your files
Drop dozens or hundreds of files that need consistent names.
Define the naming pattern
Set a base name, numbering and any find-replace rules — preview updates live.
Download the renamed set
Get all files back with clean, sequential names in a ZIP.
Filenames are more constrained than they look
Windows forbids nine characters outright — `\ / : * ? " < > |` — and reserves a set of legacy device names such as CON, PRN, AUX and COM1 that cannot be used as filenames even with an extension. macOS and Linux are more permissive, which is precisely how files that are fine on one machine become unusable on another.
Names ending in a space or a full stop are also invalid on Windows and are silently accepted elsewhere. Renaming a batch destined to be shared or uploaded is a good moment to remove those, rather than discovering the problem when someone else cannot open the file.
Numbering that sorts correctly
Alphabetical sorting is not numerical sorting. Files named 1, 2, 10 sort as 1, 10, 2, because the comparison is character by character. This is why sequences appear scrambled in file managers, upload dialogs and anything that processes a folder in order.
Padding fixes it permanently: 001, 002, 010 sort correctly everywhere. Pad to more digits than you expect to need, since extending the padding later means renaming everything again.
Dates in filenames
Writing dates as YYYY-MM-DD makes chronological order and alphabetical order the same thing. Any other arrangement — day first, month first, two-digit years — sorts by whichever component happens to come first, which is never what you want.
This is the single highest-value convention in file naming, and it costs nothing to adopt. A folder of documents named this way is permanently self-sorting in every tool that lists files.
Spaces, case and portability
Spaces in filenames require quoting in command lines and become `%20` in URLs. Hyphens or underscores avoid both, which is why anything destined for the web should use them.
Case sensitivity differs by system: Linux treats `Report.pdf` and `report.pdf` as two files, Windows and macOS usually do not. A batch that relies on case to distinguish files works on one machine and collides on another. Lowercase throughout removes the risk.
Renaming is easy to get wrong at scale
The characteristic bulk rename disaster is a pattern that produces the same name for several files, so they overwrite each other. Preview the full result before applying — every name, not the first few — and confirm the count of output names matches the count of input files.
There is no undo for a rename applied to a hundred files. Renaming a copy of the folder for anything irreplaceable is worth the extra minute. Everything runs in your browser, so filenames — which are often more revealing than people realise — are not transmitted anywhere.
Extensions and length limits
The extension is what most systems use to decide which program opens a file, so a rename that drops or mangles it produces a file the operating system no longer recognises. Any pattern applied to the whole filename rather than to the name portion will do exactly that, which is the second most common bulk rename accident after collisions.
Path length is the quieter limit. Windows historically caps a full path at 260 characters, and a long descriptive naming scheme inside a deeply nested folder reaches it faster than expected. The symptom is a file that appears to exist and cannot be opened, copied or deleted — which looks like corruption and is really arithmetic.