# 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.

**URL:** https://convertto.tech/t/file-type-identifier
**Category:** Browser & Device (https://convertto.tech/c/browser-tools)
**Privacy:** Runs entirely in the browser; no upload
**Cost:** Free, no sign-up
**Last updated:** 2026-08-01

## Key facts

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

## How to use

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

## FAQ

### 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.

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