How to open a .dat file (Windows, Mac, Linux)

Q: Why can't I open my .dat file?

Usually your computer lacks an app that understands DAT. Install one of the apps listed here, or convert the file to a more common format.

A .dat file is a Generic Data File. If double-clicking does nothing, your computer simply does not have an app that reads DAT yet. Here is how to fix that on each operating system, using free software wherever possible.

Open a .dat file step by step

Confirm the file really is a .dat. Drop it into the WhatFileType file identifier, which reads its signature without uploading anything.
On Windows, open it with The program that created it or VLC (if it is VCD video).
On Mac, use The originating program or VLC (if it is VCD video).
On Linux, try The originating program or VLC (if it is VCD video).
Still stuck? Convert the .dat to Depends on the actual contents, which opens more widely.

Best apps to open .dat files

Windows

The program that created it
VLC (if it is VCD video)
a winmail.dat reader (for Outlook TNEF)
text or hex editor (to inspect)

macOS

The originating program
VLC (if it is VCD video)
TNEF's Enough (for winmail.dat)
text or hex editor

Linux

The originating program
VLC (if it is VCD video)
tnef (command line, for winmail.dat)
hex or text editor

Web

Online winmail.dat extractors (for Outlook attachments)

Before you open it: Depends entirely on the contents. A .dat that is really plain text or video is harmless; one that is really an executable is not. Do not run a .dat, and inspect an unexpected one (or drop it into the identifier) before trusting it.

Frequently asked questions

Why can't I open my .dat file?

Almost always because no installed app understands DAT. Install one of the apps above, or convert the file to a format your existing software already reads.

How do I open a DAT file?

Find out which program created it and open it there. If you received a winmail.dat by email it is an Outlook TNEF attachment, so use a winmail.dat reader to extract the real files. If it plays as video (a VCD .dat), open it in VLC. When in doubt, drop it into the identifier or open it in a text editor to spot the real format.

What is winmail.dat and how do I open it?

winmail.dat is how Microsoft Outlook packages a message and its attachments in the proprietary TNEF format when the receiving app cannot read it. Your real files are inside. Extract them with a winmail.dat reader such as TNEF's Enough on Mac, the tnef command on Linux, or an online winmail.dat extractor. The lasting fix is asking the sender to switch Outlook from Rich Text to HTML or plain text.