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File Extension Inspector

Enter an extension or a file name to learn what the format is, which MIME type it uses and whether it deserves caution.

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What is File Extension Inspector?

A file extension hints at the format of a file and at which program will open it. This tool contains a hand-curated table of about 200 common extensions covering images, audio, video, documents, spreadsheets, archives, code, data, fonts, databases, disk images, installers and scripts, and answers instantly with no network request.

For each extension it shows a description, the usual MIME type, a category, typical programs and, where relevant, a risk note: executable programs, scripts, macro-capable Office formats, shortcuts, installers and container formats are called out. Compound extensions such as tar.gz are understood, double extensions like invoice.pdf.exe raise a warning, and anything not in the table is reported honestly as unknown instead of guessed.

How does it work?

  1. Type an extension (".psd", "tar.gz") or paste a file name; one per line for several.
  2. Read the description, MIME type, category and the programs that usually open it.
  3. Check the warning box for risk notes: executable, script, macro, shortcut, installer or container.
  4. If the extension is not listed you will be told so; use the File Inspector on the actual file for a content-based answer.

Common use cases

  • Finding out what an unfamiliar attachment or download extension means before opening it.
  • Looking up the correct MIME type for a Content-Type header or upload validation list.
  • Explaining to colleagues why .docm, .xlsm or .js files deserve extra caution.
  • Choosing which program to install or associate with a file type.

Examples

Try this input in the tool above:

Input
.psd
Output
Extension: .psd
Type: Adobe Photoshop Document
Typical MIME type: image/vnd.adobe.photoshop
Category: Image
Usually opened with: Adobe Photoshop, GIMP, Photopea

Privacy

File Extension Inspector runs entirely in your browser. The text or files you provide are processed on your device and are not uploaded, logged or stored on our servers.

Limitations

The table is deliberately limited to common extensions and gives general guidance about a type, never a verdict on a specific file: an extension can be renamed freely. For real file content use the File Inspector.

Frequently asked questions

Does a safe-looking extension mean a safe file?

No. Anyone can rename a program to .pdf or .jpg. Check the real type with the File Inspector, and be wary of double extensions such as report.pdf.exe.

Why are .docm and .xlsm flagged?

The "m" marks macro-enabled Office files, which can run code when macros are enabled. They are a classic malware carrier, so keep macros off unless you trust the sender.

What happens with an extension that is not in the list?

You get an honest "not in the built-in list" message. The tool never invents information for formats it does not know.

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