File Type Checker: Find a File's Real Format

How to check what a file really is

1. Drop one or more files onto the box above, or click Choose files. Any type and size is accepted, up to 50 files at a time.
2. Read the result under each file. Detected format names what the content really is; the badge says whether the extension matches it.
3. Check the details. For Windows programs you also see whether they are 32-bit, 64-bit or ARM, a desktop or console program, or a DLL; for ZIP files, whether they are Word, Excel, EPUB or app packages.
4. Follow the links under the result to a matching converter or to our guide for that file type.

How file signatures work

Most file formats begin with a fixed sequence of bytes, often called a magic number or file signature. Every PNG starts with the bytes 89 50 4E 47, every PDF with %PDF-, every Windows program with MZ, every ZIP-based file, including DOCX, XLSX and APK, with PK. Programs rely on these bytes, not on the file name, so they are a far better guide to the real format than the extension.

The checker reads the first 64 KB of each file and compares it with the signatures of more than 80 common formats: images, video, audio, archives, documents, disk images, fonts and executables. A few formats need a closer look, so it also reads the EBML header of Matroska files to tell MKV from WebM, the brand list of MP4-family files to tell AVIF and HEIC from MP4 video, and the file list of ZIP archives to recognise Office and app packages.

Spotting disguised programs

Windows hides known file extensions by default, so a file called invoice.pdf.exe appears as invoice.pdf. Attackers also send programs renamed to .pdf or .jpg and ask the victim to rename them back. If this checker finds a Windows executable inside a file whose extension says document or picture, it warns you in red. Do not open such a file; see how to check whether an EXE file is safe.

To always see real extensions in Windows 11, open File Explorer, choose View > Show, and tick File name extensions.

Mystery .dat and extensionless files

.dat is a generic name that dozens of programs use for their own data. The checker recognises the common kinds: Outlook's winmail.dat, Video CD tracks, Windows registry hives such as NTUSER.DAT, SQLite databases and plain text. Read our guide to .dat files for the rest.

Supported files and limitations

• Accepts any type of file.
• Up to 50 files at a time, of any size.

Only the first 64 KB of each file is read, so even huge files are checked instantly. The rest of the file is not examined.

A matching signature shows the format, not that the file is undamaged or safe. A real PDF or Office document can still contain malicious content.

Plain text formats such as CSV, INI or source code have no signature. The checker reports them as text with their encoding and recognises only formats with a clear start, such as HTML, XML, JSON or RTF.

Formats built on a common container are told apart only where the container shows it. Old .doc, .xls and .msi files share one container, as do many camera raw formats built on TIFF.

Privacy and security

Your files are opened and processed by your own browser. The ExeDepot server only delivers this page and its scripts; it never receives your files, their contents or their names. The page loads no third-party scripts or ads, and its Content Security Policy allows connections only back to exedepot.com.

Results exist only in your browser's memory until you download them, and they are discarded when you click Check more files or close the tab. No online tool can promise perfect security, so keep your browser up to date, and for documents you would never put online consider an offline desktop app such as HxD.

Frequently asked questions

How can I tell what type a file is without the extension?

Drop it onto this page. The checker identifies the format from the bytes at the start of the file, which do not depend on the name. In Windows you can also open the file in a hex editor such as HxD and compare the first bytes with a list of signatures.

Is it safe to rename a file to its real extension?

Yes, renaming changes nothing inside the file. If the checker says a .jpg is really a PNG, renaming it to .png simply lets Windows choose the right program. Never rename a file to .exe, .bat or .scr unless you trust where it came from.

Can this tool tell if a file has a virus?

No. It identifies formats; it does not scan for malware. It does flag programs disguised as documents, which is a common trick. To scan a file, use your antivirus; see our guide to free antivirus software.

Are my files uploaded?

No. Only the first 64 KB of each file is read, by a script in your browser. Nothing leaves your device.