Skip to content
Convertto

What Type of File Is This? — Identify by Signature, Not Extension

Identify any file from its magic bytes, and see whether the extension is telling the truth.

A file's real type is in its first few bytes, not its extension. This reads the leading 64 bytes of each file and matches them against known signatures — PNG starts with 89 50 4E 47, PDF with %PDF, every ZIP-based format with PK — then flags any file whose extension disagrees with what the bytes say.

Runs in your browser
Privacy
Runs entirely in your browser — nothing is uploaded
Cost
Free, unlimited, no sign-up

Frequently asked questions

Why does my DOCX show up as a ZIP archive?

Because it is one. Every Office Open XML file — DOCX, XLSX, PPTX — plus EPUB, JAR and APK is a ZIP containing XML and media. The signature is genuinely PK, and only the internal structure distinguishes them, which is why this reports the container honestly rather than guessing.

Does a mismatch mean the file is malicious?

Not by itself. Renaming a file is common and harmless. It matters when the mismatch is designed to deceive — an executable named .jpg, for instance. The check tells you what the bytes say; the significance depends on where the file came from.

Why is my text file not recognised?

Plain text, CSV, JSON, HTML and source code have no signature — there is nothing distinctive at the start of the file to match. "Not recognised" for a small file almost always means text.

How to use the file type identifier

  1. 1Select your files — the file stays on your device and is never uploaded.
  2. 2Turn "Show the raw header bytes" on or off as needed.
  3. 3Press Run, then download the result when it is ready.

Embed this tool

Put the working file type identifier on your own site. It runs in your visitors' browsers exactly as it does here — free, no account, nothing uploaded.

Share this tool

Related tools

Base64 to File ConverterDecode Base64, a data URI or hex back into a downloadable file, with the type detected automatically.HMAC GeneratorGenerate an HMAC signature with SHA-256, SHA-1, SHA-384 or SHA-512 and a secret key.JWT VerifierVerify a JWT's HS256 signature and its expiry, issuer and audience claims, entirely in your browser.MIME Type LookupFind the correct MIME type for any file extension, and vice versa.Quoted-Printable Encoder & DecoderEncode and decode quoted-printable, the MIME format used in email bodies and headers.Sign PDF DocumentDraw your signature, drag it onto the page and save a signed PDF — without uploading anything.

Last updated

More browser & device