File Type Detector

What this tool does

File Type Detector reads a file’s first few bytes and matches them against a table of known magic-byte signatures (the same technique the Unix `file` command uses) to identify its real content type, flagging any mismatch against its file extension, a common sign of a renamed, corrupted, or mislabeled file.

A file’s extension is just a naming convention, anyone (or any process) can rename a .jpg to .txt without changing its actual content, which is why relying on the extension alone to know what a file really is isn’t fully reliable.

This detector instead reads the file’s first few bytes, its "magic number", and matches them against a table of known signatures covering images, archives, documents, audio, video and more, the same fundamental technique the Unix `file` command uses, then flags clearly if the detected type doesn’t match the file’s extension.

How to use File Type Detector

1. Choose a file to analyse.
2. Review the Detected type result.
3. Check for a mismatch warning against the file’s extension.
4. Inspect the raw first 32 bytes in hex if you need to investigate further.

Tips for better results

• A mismatch warning doesn’t always mean something malicious, it’s equally often just a file renamed by accident, a failed or partial download, or a format the detector’s signature table doesn’t cover.
• Several common formats (like .docx, .xlsx and .pptx) are internally just ZIP archives, so they correctly detect as "ZIP archive" at the byte level, that’s expected, not a mismatch to worry about.
• An "unrecognised" result doesn’t mean the file is invalid, it just means its signature isn’t in this detector’s table, many plain text-based formats have no distinctive magic bytes at all.
• Only the first 32 bytes are read, so this is a fast, lightweight check, not a full file integrity validation.

Common use cases

• Verifying a downloaded file is actually the type it claims to be before opening it.
• Investigating why a file with a given extension won’t open correctly in its expected application.
• Checking a batch of files for extension mismatches after a bulk download or extraction.
• Learning how magic-byte file type detection works with real, concrete examples.

Common mistakes to avoid

• Treating "unrecognised" as proof a file is corrupted or fake; many legitimate formats (especially plain text-based ones) simply have no distinctive magic-byte signature to detect.
• Being alarmed that a .docx or .xlsx file detects as a "ZIP archive"; that’s correct and expected, since those Office formats are internally ZIP containers.
• Assuming this check guarantees a file is safe; magic-byte detection identifies format, not malicious content hidden within a file that is otherwise a genuinely valid example of its detected type.