What is an ATT file?
An .ATT file is most commonly a generic email attachment. This happens when email clients like Microsoft Outlook or web forms process data but fail to preserve the original file extension. Under the hood, an .ATT file is often a standard format like a .PDF, .JPG, .ZIP, or .DOC document.
Beyond emails, the .ATT extension serves as a configuration or data file for specific software. For example, PTV Vissim uses .ATT files to store traffic simulation results and attributes. Other uses include interaction configuration files for telecommunication systems by Cisco, game map attributes for MU Online, and CAD attributes for Asuni CAD Lands Design.
How to open ATT files?
Because the .ATT extension has multiple possible meanings, guessing the correct software is difficult. If you know the original format of an email attachment, you can sometimes rename the extension (for example, from file.att to file.pdf) and open it with your default viewer. However, if the origin is unknown, this trial-and-error method is inefficient.
We recommend using viewer.online/att to inspect your file safely. The platform analyzes .ATT files to identify their exact format and creator software, shows which programs can open the file, and usually previews it immediately.
Best practices and troubleshooting
If you frequently receive .ATT files via email, ask the sender to check their email client settings. Often, changing the outgoing mail format from Rich Text to HTML or Plain Text prevents attachments from converting into generic .ATT or .DAT files.
Since .ATT files hide the true identity of the data, they can pose a security risk if they contain executable code. Do not open or rename attachments from unknown senders. Once you know the actual format of your .ATT file, you can use convert.guru to convert it to standard target formats like .PDF, .DOCX, or .JPG for easier sharing.
Summary
viewer.online/att directly opens and previews .ATT files in the browser, eliminating the need to install software or troubleshoot compatibility issues.