PDF Mikata

Check a File's Real Type (Extension vs Contents)

To find out what a file that will not open really is.

Your files are never uploaded. Everything is processed on this device.

  1. 1Choose files
  2. 2See the result
  3. 3Copy the result
Done

🔒 Your files are never sent to an external server. Everything is processed safely inside this browser.

How to use

  1. Tap "Choose files" and select the files to check (several allowed).
  2. A table shows the type judged from the contents and whether the extension matches.
  3. Use "Copy the result" if you need the results.

How it works

  • It reads the identifying mark at the start of a file (the magic number).
  • docx, xlsx and pptx are told apart by looking inside the ZIP.
  • Text is judged by whether it reads as characters.
  • Unsupported formats are shown as "Unknown".

Notes

  • Changing an extension does not change the contents. A file with only its extension changed may not open.
  • Formats that cannot be judged are shown as "Unknown".
  • It cannot tell whether a file is dangerous.

FAQ

Are my files uploaded anywhere?

No. Everything is processed inside the browser on your device.

What if the extension does not match?

Change it to the extension for the real type and reopen the file. Rename Many Files at Once can help.

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Guides for this tool

How to Find a File's Real Type (Extension vs Contents)Finding Out What a File That Will Not Open Really IsWhat to Watch for When an Extension and Contents DifferTelling docx, xlsx and pptx ApartChecking Whether a Photo That Will Not Open Is HEICWhich Types Can Be Detected and the LimitsChecking a File's Type Without Uploading It

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