Identify a file
Not sure what that mystery .dat, extension-less download, or renamed file actually is? Drop it below — we read the first 16 bytes and match them against the binary signature of every format in our encyclopedia. Your file is never uploaded; everything happens in this browser tab.
Drop a file here, or click to choose one
Nothing is uploaded — the file never leaves your device.
How this works
Most archive and compression formats begin with a fixed magic byte sequence — a short signature that identifies the format regardless of what the file is named. A ZIP-based file always starts with 50 4B 03 04; a gzip stream always starts with 1F 8B; a 7z archive always starts with 37 7A BC AF 27 1C. This tool reads only the first 16 bytes of the file you choose (using the browser's File API, entirely offline), converts them to hex, and compares them against the signature of every format tracked on this site.
Some formats — plain-text containers, some disk images, a few legacy or headerless formats — do not have a reliable fixed signature. For those we fall back to matching on the file extension instead, and say so explicitly.
Several packaging formats are literally ZIP archives with extra metadata (APK, JAR, DOCX, EPUB, XPI and more all share the 50 4B 03 04 signature), so when a signature is shared by multiple formats, this tool lists all of them and uses your file's extension as the tiebreaker.
Frequently asked questions
Does this upload my file anywhere?
No. The file is read locally using the browser's FileReader API. No network request is made with your file's contents — the only network request this page makes is fetching our public signature database on load, before you pick anything.
Why does it only read 16 bytes?
Every signature in our database is 12 bytes or shorter, so 16 bytes is enough to match any of them while keeping the check instant, even on a huge file.
What if my file isn't recognized?
It may be a format we don't track yet, a corrupted or truncated download, or not an archive at all. Browse the full list of 220+ formats to check manually, or contact us if you think we're missing something common.