File Type Checker
Find the real format of a file with a wrong or missing extension
🔒 Files are checked entirely in your browser — nothing is uploaded.
Drop a file with a wrong or missing extension, or click to choose
You can check several files at once
You can check several files at once
※ The tool reads the file signature (magic number) at the start of the file. Only the extension changes — the contents stay exactly the same.
Common cases
| Saved as | Usually really |
|---|---|
| download.php · download.aspx | PDF, images, Office files |
| download.do · FileDown.do (Java sites) | PDF, HWP, XLSX, ZIP |
| getImage.do · image.php | JPG, PNG |
| No extension (file, attachment) | Anything — check it |
Formats it can identify
.jpg.png.gif.webp.heic.avif.bmp.svg.pdf.hwp.hwpx.docx.xlsx.pptx.doc.xls.ppt.zip.7z.rar.mp4.mov.mp3.wav.html.csv.txt.json.xml.exe
FAQ
Why did my download save as .do, .php or .aspx?
Many websites send files through a script address such as
download.php, download.aspx or download.do. When the server does not send a proper file name, the browser uses the last part of the address as the name. The file inside is usually a normal PDF, image or document.Can I just rename the extension?
Yes — once you know the real format, renaming fixes it. This tool reads the file signature to tell you the exact format and saves a copy with the right extension.
It says the file is a web page (HTML)
The site saved an error or login page instead of the file. This happens when a session expired, you lack permission or a pop-up was blocked. Sign in again and retry the download.
Are my files uploaded?
No. Files are read and processed only inside your browser. Nothing is stored or sent anywhere.
Does it work on phones?
Yes. Pick the file from the Files app (iPhone) or My Files (Android). The fixed copy is saved to your downloads with the new name.