Why do you not just add a virus scanner?

A real virus scan needs a continuously-updated signature database, sandbox execution, and behavioural heuristics. We would either ship a stale local model (worse than no signal at all) or send your file to a third-party scanner (defeats the privacy promise). Neither trade-off is worth it for the value we add.

Can a MATCH ever be wrong about safety?

Yes, by design. A MATCH only confirms format identity. A correctly-formatted PDF can still embed JavaScript that exploits a viewer; a correctly-formatted DOCX can still ship malicious macros. Format and safety are independent concerns.

What should I do with a MISMATCH verdict?

Treat it as a strong reason to slow down. Confirm with the sender that the file is what the name claims, or open the file in a sandbox / virtual machine you do not mind losing. Do not double-click on instinct.

Does the File Type Checker open the file at all?

It reads the first 4096 bytes to look up the magic-byte signature, and on desktop it runs an AI content classifier on text-like files. It never executes embedded scripts, never follows external URLs in the file, and never uploads the bytes anywhere on the free single-file flow.

Is my file safe?

A magic-byte check identifies what a file is, not whether it is dangerous. This page sets the boundary up front so you know when our File Type Checker helps and when you still need an antivirus.

Open the File Type Checker See what it answers

Honest scope
No malware scan
Bytes never leave your browser

Key facts

What it answers
Format identity. Does the byte content match what the extension claims? MATCH, MISMATCH, AMBIGUOUS, or UNKNOWN.
What it does not answer
Malware. The checker does not unpack archives, does not run macros, and does not call out to a third-party virus database.
How to use it
Treat a MISMATCH as a strong "look closer" signal. Treat a MATCH as "the format is what it claims", not "the contents are safe".
Pair with antivirus
For an actual safety verdict, run the file through your endpoint security or upload to a multi-engine scanner. The two checks complement each other.

Short answer: a magic-byte check cannot tell you that. What it can tell you is whether the file is the kind of file its extension claims it to be. That is a useful first signal, but it is not a safety verdict.

What our File Type Checker actually answers

Does the first byte sequence match the format the extension suggests? (PDF, PNG, ZIP, Word document, etc.)
If the magic bytes do not match, is the detected format compatible with the extension or not?
For text files with no magic-byte signature, an AI content classifier identifies the content type locally on desktop.

What it does NOT answer

Whether the file contains malicious payloads (we do not run a malware scanner; we do not call out to a third-party scanning service).
Whether macros, embedded scripts, or remote content inside a document are dangerous.
Whether an encrypted archive is harmless (we cannot read encrypted contents).

Not a malware scanner

A MATCH verdict says "the bytes look like the format claimed". It does not say "the contents are safe to open". Always pair this check with a real antivirus when the file came from somewhere you do not fully trust.

How to use this in practice

If you receive an attachment that "feels off", drop it here first. A MISMATCH verdict is a strong signal that something has been relabelled and you should double-check with the sender. A MATCH verdict tells you the bytes look like the format claimed; it does not promise the contents are benign.

For a malware verdict, use a real antivirus / EDR product. The File Type Checker is a complementary tool, not a replacement.

Frequently asked questions

Try the verdict for yourself

Drop any file. The check runs in your browser, returns one of four verdicts in under a second, and never uploads anything on the free flow.

Open the File Type Checker