File Type Identifier
Detect a file's real type by reading its first bytes and matching against known magic-number signatures, entirely in your browser.
How the File Type Identifier Works
Choose a file and the tool reads its first 16 bytes directly using your browser's FileReader API, then compares them against a table of known "magic number" signatures — fixed byte patterns that most file formats begin with, such as PNG's 89 50 4E 47, PDF's 25 50 44 46, or a Windows executable's 4D 5A. Because it inspects actual file content rather than the file name, it correctly identifies a file's real type even if its extension is wrong, missing, or was changed on purpose.
The file is read entirely in your browser using local JavaScript — nothing is ever uploaded to a server.
Example
A file renamed from photo.png to photo.txt will still show its first bytes as 89 50 4E 47 and be correctly identified as a PNG Image, regardless of the misleading.txt extension.
Common Use Cases
- Verifying what a downloaded file actually is before opening it, especially if its extension looks suspicious.
- Recovering the real type of a file that lost or never had a proper extension.
- Confirming a file wasn't corrupted or mislabeled during a transfer or export.
FAQs
- How is this different from the File Extension Finder? The File Extension Finder is a static name-to-type lookup table — you type an extension like ".docx" and get its description. This File Type Identifier actually inspects the real bytes of an uploaded file, so it works correctly even when the extension is wrong, missing, or was deliberately changed.
- Is my file uploaded anywhere? No — the file is read entirely client-side in your browser using the FileReader API. Nothing is sent to a server at any point.
- Why did my file show "no known signature matched"? Some file types (like plain text, CSV, or certain proprietary formats) don't start with a distinctive byte pattern, or use a signature not included in this tool's reference table.