DAT File Viewer — Open & Read .DAT Files Online Free

The .dat file extension is one of the most ambiguous in computing — it is used by hundreds of different applications with no standard internal structure. The four most common varieties are: Winmail.dat email attachments created by Microsoft Outlook (using the TNEF format), application configuration and settings files, game save and level data files from PC games, and VCD video data files (typically named AVSEQ01.DAT) containing MPEG-1 video. Because the extension alone tells you nothing about the content, being able to quickly peek inside a .dat file is an essential diagnostic skill.

This online DAT file viewer uses the browser's built-in FileReader API to open your file entirely on your device — nothing is uploaded to any server. Once loaded, it automatically detects whether the file is text-based or binary. Text-based files (such as config files or readable game saves) are shown in the Text view, where you can read and copy the raw content. Binary files are shown in a professional Hex view that displays the byte offset, hexadecimal byte values in two groups of eight, and the printable ASCII representation side by side — the same layout used by dedicated hex editors like HexEd.it or HxD.

The most common use cases for this tool are: inspecting a mystery .dat file to determine which application created it, reading a plain-text config or settings file without installing a text editor, checking what text is visible inside a Winmail.dat email attachment, and examining binary game save data to understand its structure. Because all processing runs locally in your browser, files of any size can be opened without network delays, and your data stays completely private.