Rename a batch of files
Point it at a folder, describe the naming pattern you want, and it renames the files. On a browser that supports the File System Access API it renames the actual files on your disk — nothing is uploaded and nothing is copied anywhere.
Pattern tokens: {name} original name without extension, {n} number, {ext} extension without the dot. The original extension is appended automatically — unless your pattern contains {ext}, in which case you are in control of it.
| Current name | New name |
|---|
Why the browser can do this now
For most of the web's history, a page could read a file you handed it but had no way to write one back, which is why every "online batch renamer" ever built worked by making you download a zip of copies. That is not renaming — it is duplicating with extra steps, and it leaves you to delete the originals yourself.
The File System Access API changed this. A page can now ask for access to a folder, list what is in it, and rename entries in place. The permission is granted by you, per folder, and the browser makes it visible that a page has access. It is a genuinely different capability from uploading.
Two consequences worth knowing:
- Renaming is instant and lossless — the file is not read, re-encoded or rewritten, only its directory entry changes. A four gigabyte video renames in the same time as a text file.
- Browser support is not universal. Chrome, Edge and Opera support it; Safari and Firefox do not, as of writing. On those browsers this tool falls back to producing renamed copies you download.
Naming patterns that age well
Most renaming pain is caused by decisions that look fine on twenty files and terrible on two thousand. The patterns that survive contact with a real archive share a few properties.
Zero-pad the numbers
Without padding you get file-1, file-10, file-2 — because sorting is alphabetical, not numerical. The files end up in an order that looks shuffled. With two digits you get file-01 through file-10 sorting correctly. Use enough digits for the largest number you can imagine reaching: two for under a hundred, three for under a thousand.
Put the date first, as YYYY-MM-DD
Dates written any other way sort wrongly. 03-02-2026 is ambiguous between March 2nd and February 3rd depending on where you are. 2026-02-03 sorts correctly as text and reads unambiguously to everyone.
Avoid spaces and punctuation
Spaces in filenames cause endless minor trouble: they become %20 in URLs, need quoting in every command line, and are inconsistently handled by scripts. Hyphens and underscores are the safe separators, and hyphens read better in anything that will eventually be published on the web.
Pick a separator and never mix
If some files use _ and others use -, search and sort stop working the way you expect. Decide once.
Keep the extension out of the pattern
The tool never changes the extension, because changing it usually breaks the file: renaming photo.jpg to photo.png does not convert it, it just makes a JPEG that lies about its type. Extensions are metadata about the format, not part of the name you are designing.
Characters that are not allowed in filenames
Opera
| Character | Where it breaks |
|---|---|
/ | Path separator on every system |
\ : * ? " < > | | Forbidden on Windows; some are interpreted specially |
: | Forbidden on Windows and in macOS, where the Finder converts it to / |
| Leading or trailing spaces | Silently stripped by Windows and by many download tools |
| Trailing dots | Also stripped on Windows |
Names ending in .nul .con .prn | Reserved device names on Windows, at any extension |
| Leading hyphen | Read as an option flag by command line tools |
| Emoji and other non-ASCII | Legally fine on modern systems, but breaks on older tooling, network shares and zip archives from other platforms |
Windows also caps the full path at around 260 characters unless it is configured otherwise, which means a long pattern plus a deeply nested folder can produce files that cannot be created at all. If a rename silently fails on Windows, this is the first thing to suspect.
A rename is not a conversion
The most common misuse of a bulk renamer is using it to change format. Renaming image.webp to image.jpg does not make it a JPEG. Most programs look at the file's content rather than its name and will either open it fine or refuse it, but anything that trusts the extension — an upload form, a build script, a camera import — will now be misled.
If the actual format needs to change, use the format converter first and rename the results afterwards. That order works; the reverse does not.
Questions
Are my files uploaded?
No. Renaming uses the browser's File System Access API, which operates directly on your disk after you grant permission for a folder. The file contents are never transmitted. The download-based fallback works on copies held in memory and leaves the originals alone.
What happens if two files would get the same name?
The tool detects it before anything is changed and refuses to run, listing the collisions. This matters because a rename that produces duplicates could otherwise overwrite a file. Fix the pattern — usually the missing element is {n}, or an existing name that the pattern reproduces.
Does it rename folders as well as files?
No, files only. Renaming directories is a riskier operation because the paths of everything inside them change with it, and a mistake is far harder to undo.
Can I undo a batch rename?
Not with this tool. The cleanest safety net is to run the rename on a copy of the folder the first time, or to export the before-and-after list the tool shows you. Keeping the list is also useful for finding files again if a pattern turns out to be wrong.
Why does it not work in Safari or Firefox?
Because those browsers do not implement the File System Access API, and without it a web page has no way to rename a file in place. The tool detects this and switches to producing renamed copies for download instead of failing.