How to Batch-Rename Files in Your Browser: Bulk File Renamer
Reviewed by the OnlineFree.app team · Updated
Key points
- Bulk File Renamer renames local files in the browser and returns them as one ZIP — nothing is uploaded.
- It applies one rule set at a time: find & replace, added numbers, or a case change such as kebab-case.
- The preview table marks clean rows green and conflicts amber, including collisions and illegal characters.
- Renaming changes filenames only; the contents inside the ZIP stay byte-for-byte identical.
- Your original files on disk are never modified, so a bad rule costs a re-download, not your data.
How do you batch-rename files without uploading them?
Bulk File Renamer is a free browser tool at OnlineFree.app that renames many local files in one pass — find & replace, sequential numbering, or a case change — then hands them back as a single ZIP. Nothing is uploaded and no account is required.
The detail that matters is where the work happens. When you add files, Bulk File Renamer reads only the filenames and extensions to build the old → new preview. The file bytes stay in your browser tab and are touched only at download time, when the ZIP is assembled on your own device. That is ordinary browser behaviour under the standard File API, which exposes a file to a page only after you choose it.
That makes the tool a sensible fit for folders you would rather not hand to someone else's server: scanned contracts, client photos, screenshots, or unreleased design assets. It also sits alongside other free online tools on the same site if you are tidying a whole project.
Step-by-step: rename a folder of files
Open the Bulk File Renamer page and drop your files onto the zone at the top, or click the zone to pick them from a file dialog. The preview table fills immediately with one row per file, showing the current name on the left and the proposed name on the right.
Choose one mode — Find & Replace, Add Numbers, or Change Case — and fill in the fields that appear for it. Only one rule set runs at a time, so pick the change that matters most, or plan to run the folder through twice.
If you picked Add Numbers, the start index box appears (it defaults to 1). Set the prefix or suffix, the separator, and the padding — a 3-digit padding turns a run into 001, 002, 003 rather than 1, 2, 3. Padding matters most when you sort by name later, because 10 sorts before 2 without it.
Scan the table row by row, fix anything flagged amber, then hit the sticky Download ZIP button. If you only want one or two of the renamed files, the secondary 'Download individually' link gives you single files instead of the archive.
Choosing between find & replace, numbers, and case
Find & Replace is the workhorse. You enter the text to find and the text to replace it with, toggle case sensitivity, and choose whether the rule applies to the filename, the extension, or both. A typical run: find IMG_ and replace with hawaii-2026-, turning IMG_2043.jpg into hawaii-2026-2043.jpg. Leaving the rule on the name only is the safe default; touching the extension is how people accidentally produce files their operating system no longer opens.
Add Numbers appends or prepends a sequence, which is what you want for scans, receipts, lecture slides, and photo exports that arrived without useful names. Combining a short prefix with the numbering gives you ordered, self-describing files like invoice-acme-001.pdf.
Change Case covers lowercase, UPPERCASE, Capitalize, kebab-case and snake_case. Kebab-case and snake_case are the useful pair for web and code assets, because spaces in filenames have to be encoded as %20 in URLs. The preview shows exactly what a case rule does to the whole string before you commit, so check the extension column carefully if your filenames contain dots.
Read the preview table before you commit
Every row shows the old name in a monospace cell next to the proposed name, with a green check on rows that will rename cleanly and an amber warning on rows that will not. The counter above the table reports how many files will change and how many will stay as they are — a useful sanity check, because a find-and-replace that matches nothing leaves the count at zero renamed.
Three warning types are worth knowing. An empty name means your rule stripped everything out of the filename. An illegal character means the result contains something the target system refuses — on Windows, characters such as < > : " / \ | ? * are not allowed in filenames, and names cannot end in a period or space, per Microsoft's naming conventions for files and paths. A collision means two files would end up with the same name.
Collisions are the most common surprise. Replacing a long shared prefix with nothing often merges files that only differed by that prefix, so the preview flags them instead of quietly overwriting. Adjust the find text, add a numbering pass, or remove one file from the list.
What the ZIP download does and does not do
The primary button packages every listed file under its new name into one .zip and downloads it in a single transfer. Contents are untouched: the bytes inside each file are identical to what you supplied, so image dimensions, document text and code stay exactly as they were. Renaming is a label change, not a conversion, and the tool does not re-compress or re-encode your data.
One consequence is worth flagging. If you changed the extension as part of a find & replace rule, the file contents will still match the old type, and your operating system may warn or fail to open the result. Bulk File Renamer renames; it does not transcode.
Because the archive is generated in your browser, very large folders are limited by your device's available memory rather than by a server quota. Original files on your disk are never modified — the ZIP is a separate copy, so a mistake costs you a re-download, not your data.
Common mistakes and honest limits
The biggest slip is leaving 'apply to extension' switched on while doing a text replacement, which can mangle .jpg, .pdf or .csv endings across a whole batch. The second is renaming without padding, producing files that sort in the wrong order in every file manager you use afterwards. Both are visible in the preview if you read it, which is why the preview exists.
Be realistic about what the tool does not do. It cannot chain rules in one run, it holds no history, and there is no undo button — you correct a bad rule by editing the rule, not by reverting. It also does not write directly back into your folder; you get a ZIP and unzip it yourself.
Finally, treat the preview as advisory rather than infallible. The collision and illegal-character checks catch the common cases, but if a filename matters for a build script, a CMS upload, or a legal archive, verify the result after unzipping rather than assuming it.
Frequently asked questions
Does Bulk File Renamer upload my files to a server?
No. Bulk File Renamer runs entirely inside your browser. Only the file names and extensions are read to build the old → new preview, and the file contents are used solely to package the ZIP on your own device at download time. Nothing is uploaded, no account is needed, and no copy is stored remotely.
Can I combine find & replace, numbering and case changes in one pass?
No. Bulk File Renamer applies one rule set at a time: Find & Replace, Add Numbers, or Change Case. To both renumber and lowercase a folder, run the files through twice, or rename once, unzip the download and feed the results back into the tool for the second change.
Does renaming change the contents of the files?
No. The ZIP download contains your original files byte for byte, filed under their new names. Image dimensions, document text and code stay identical, because renaming changes only the label. The one exception to watch is a rule that edits the extension — the name changes, but the file type inside does not.
What happens if two files would end up with the same name?
Bulk File Renamer flags the row in amber in the preview table instead of silently overwriting anything. You then fix it by adjusting the find text, adding a numbering pass, or removing one file from the list. Correct the rule first, then download the ZIP.
Is Bulk File Renamer free, and is there a file limit?
It is free and requires no sign-up, email or account. Because the ZIP is assembled on your own device rather than on a server, there is no server-side file-count limit; the practical ceiling is your browser's available memory with very large folders.