Why Is My File Type Wrong
Why it happens
Why is my file type wrong? The most common reason is that the filename extension does not match what is inside the file. A file can be renamed from .png to .jpg, but the internal bytes may still look like a PNG.
MIME type detection can also differ between browsers, operating systems, and upload systems. Some tools trust the extension, some inspect the file header, and some use both.
How to check it
Start with MIME Type Checker to see what the browser and file properties report. Then use File Signature Checker to inspect the first bytes of the file and compare the signature with the extension.
If the extension, MIME type, and signature agree, the file is probably labeled correctly. If they disagree, the file may have been renamed, exported incorrectly, wrapped in a container, or damaged.
How to fix it
If the file was only renamed, use the correct extension for the format shown by the signature. If an upload form requires a different format, re-export or convert from the original app instead of changing the filename only.
For documents, images, audio, and video, open the file in the relevant metadata viewer when you need more context about codec, document properties, dimensions, or container details.
How to prevent it
Export files directly into the required format and avoid manual extension changes. When a site has strict upload rules, check the file type before submitting it.
Keep an original copy so you can re-export cleanly if a file type mismatch appears during upload or review.