How to Inspect a File's Type and Details

A file with no extension, a download you are not sure about, an attachment that will not open — sometimes you need to know what a file *actually is* before you trust or use it. A file inspector reads a file's real details: its true type, size, and metadata. This guide explains why the extension can lie, what inspection reveals, and how it helps you stay safe and solve problems.

Why the extension is not the truth

A file's extension — `.pdf`, `.jpg`, `.docx` — is just part of its name, and names can be anything. The *real* type is determined by the file's actual contents, specifically the "magic number" or signature in its opening bytes. A file called `photo.jpg` might really be something else entirely, and a file with no extension still has a true type baked into its data. Inspection reads that real signature rather than trusting the label.

How to inspect a file with this tool

1. Open the File Inspector tool.
2. Load the file.
3. Read its detected type, size, and details.

Everything runs in your browser, so the file is never uploaded — you can safely examine something suspicious without sending it anywhere.

What inspection tells you

• The real file type, detected from the content signature, not the extension.
• The exact size in bytes.
• Format details and metadata the file carries.

This answers the practical questions: What is this thing? Is it what it claims to be? Will the program I am about to open it in understand it?

Where inspection matters most

• Security. A file named `invoice.pdf` that inspection reveals to be an executable is a warning sign. Disguised file types are a common malware trick, and checking the true type before opening is a real defense.
• Identifying mystery files. A file with no extension, or an unfamiliar one, becomes usable once you know what it actually is and can rename or open it correctly.
• Troubleshooting. A file that "won't open" is often mislabeled — inspection shows the true format so you can use the right program or fix the extension.
• Confirming a download or transfer arrived intact and as the expected type.

Related tools

If inspection shows the file is an archive, Zip Extractor unpacks it. If it is encrypted, Decrypt File restores it. Reassembled a file from parts with File Merger and want to confirm it is whole and correct? Inspect it here.

Common uses

• Identify an unknown or extensionless file.
• Check a file is what it claims before opening.
• Spot disguised file types.
• Troubleshoot a file that will not open.

Privacy and limits

Inspection is fully local — no upload, no file-size cap, nothing stored, offline once loaded. Open the File Inspector tool to see what a file really is.