File Extension Changer
Rename the extensions of files you drop, without touching their contents: replace an extension, add one, remove it, make it lower case, or let the tool pick the extension that matches the file’s real format. Each file’s content is checked against its new name, so you are warned when renaming would mislabel it, and renaming to executable or macro types is blocked.
- Runs in your browser
- No sign-up
- Free to use
| File | New name | Content check |
|---|
How to use File Extension Changer
- Drop the files whose extensions you want to change.
- Choose the change and, if needed, the new extension.
- Check the content column for mismatches.
- Rename and download the files or a ZIP.
File Extension Changer features
Five actions
Replace, add, remove, lower-case or fix from content.
Content check
Reads each file’s signature to see what it really is.
Fix wrong extensions
Gives a .txt that is really a PNG its proper .png.
Safety
Blocks renaming to .exe, .bat, .js, .ps1, macro documents and similar.
Unchanged contents
Files are byte-for-byte identical after renaming.
Local
Up to 50 files; nothing is uploaded.
When to use File Extension Changer
- Fixing images that were saved with the wrong extension.
- Turning .TXT and .JPG into lower-case extensions for a web server.
- Removing a duplicated extension such as report.pdf.pdf.
- Restoring the extension of downloads that arrived without one.
File Extension Changer FAQ
Does changing the extension convert the file?
No. The extension is only part of the name. A Word document renamed to .pdf is still a Word document; use a converter to change the format.
What does the content check do?
It reads the first bytes of each file, its signature, to identify the real format and compares it with the new extension.
Why can I not rename to .exe or .js?
Giving a file an executable extension could make it run when opened, and mislabelled programs are a common malware trick. The tool blocks these extensions on purpose.
Is my file changed?
Only its name. The downloaded file has exactly the same bytes as the original.
Can I rename files on my computer directly?
Browsers cannot rename files in place. Download the renamed copies, or use the File Name Generator’s rename script.
Are my files uploaded?
No. Everything happens in your browser.
What an extension is, and what it is not
A file extension, the letters after the last dot, tells the operating system which program should open a file. It is a label, not a property of the data. That is why renaming can fix problems, such as an image that arrived as image.jpg.txt, and also why it can cause them, such as a spreadsheet renamed to .pdf that no PDF reader can open.
This tool changes labels carefully. For every file it reads the first bytes, the signature that most formats begin with, and identifies the real content: a PNG starts with a fixed eight-byte sequence, a PDF with %PDF, a ZIP-based Office document with PK and a recognisable structure. The new name is then compared with that content, and a mismatch is flagged before anything is downloaded.
The “use the extension that matches the content” action does the reverse: it looks at what each file really is and gives it the standard extension for that format. It is the quickest way to repair downloads and exports that lost or garbled their extensions.
Some extensions are blocked. Executables, scripts, shortcuts, disk images and macro-enabled Office documents can run code when opened, and giving such an extension to a file is a classic way to disguise malware or to run something by mistake. Renaming to those types is not offered.
Browsers cannot rename files on your disk, so the tool produces renamed copies to download individually or as a ZIP. The contents are identical to the originals byte for byte, and nothing is uploaded.