Identifying a file type is often very easy. A glance at the icon gives you a general idea – VLC Media Player tells you it’s a media file, for instance – and the extension tells you everything else.

Life isn’t always that simple, though. File extensions might be lost, changed, or maybe you’ve just found a mystery file in a folder somewhere and would like to know what it is.

Opening the file in Notepad can give you some clues. If the first two characters are MZ, it’s a Windows executable; PK means a ZIP file; ID3 is a media file; 6 cryptic bytes followed by JFIF signifies a JPG, and so on.

TrIDNet is a free-for-personal-use tool which uses the same principle to identify file types by their content alone. It’s been around for a long time, but is the program still relevant today? We grabbed a copy to find out.

Setup is a two-step process. There’s no installation, but after downloading and unzipping TrIDNet.exe you must download its file definitions separately, and unzip them into the same folder (you’ll have a \defs folder in the same folder as TrIDNet.exe).

TrIDNet not only recognised that this test file was a ZIP, it also spotted that it was a Word DOCX file

With that out of the way, importing test files is as easy as dragging and dropping them onto the TrIDNet.exe window. The results are displayed in a table.

Sometimes the program offers a single verdict – our test RAR was 100% a “RAR Archive” – but you’ll often see extra information.

We imported a Word DOCX and were told it was 85.5% a “Word Microsoft Office Open XML Format document”, and 14.5% a “ZIP compressed archive”. That’s impressive, because DOCX files are structured as ZIPs with word processing documents inside, so TrID-Net has told you almost everything you need to know.

(And if you need to know more, double-clicking the column header opens a dialog with additional details, including – in the case of DOCX – a link to Wikipedia’s page on the format.)

That’s a very common format, of course, so we tested the program with assorted leftovers that we’d found in our Documents folder.

Picate.pixate was a remnant of the old Pixate project, but TrIDNet revealed that it was also a regular SQLite 3.x database, so we should be able to view it in any SQLite app.

TrIDNet next explained that MyData.p2g was a part of a Power2Go project, useful in deciding whether it could be safely deleted.

The program can’t replace human expertise entirely. If you understand SQL then you’ll recognise a .SQL dump immediately, but TrIDNet won’t because the file type doesn’t have a fixed signature it can use.

But when there are signatures available, the program does very well. We give it an MSI and not only did it tell us this was a Windows Installer file, it also gave us the overall type: a generic OLE2/ Multistream Compound File.

TrIDNet doesn’t have any batch processing support, but the console-based TrID.exe has a few related options. If you’ve undeleted a bunch of files which no longer have their signatures, for instance, running a command like trid \recovered\* -ae will rename them all to have the best-guess extension– potentially very useful.

TrIDNet is available for Windows XP and later.