What Is a CAP File?

Lots of formats use this extension. Here's how to open all of them

By
Tim Fisher
Photo of Tim Fisher, Lifewire GM and Writer
Tim Fisher
Senior Vice President & Group General Manager, Tech & Sustainability
  • Emporia State University

Tim Fisher has more than 30 years' of professional technology experience. He's been writing about tech for more than two decades and serves as the SVP and General Manager of Lifewire.

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Updated on April 19, 2022
Reviewed by
Ryan Perian
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Reviewed by Ryan Perian
  • Western Governors University
Ryan Perian is a certified IT specialist who holds numerous IT certifications and has 12+ years' experience working in the IT industry support and management positions.
lifewire's editorial guidelines

What to Know

  • Some CAP files are packet capture files.
  • Those files open with Wireshark.
  • Convert one to HCCAPX with hashcat, or to TXT with Wireshark.

This article details the several formats that use the CAP file extension, and how to open each type.

What Is a CAP File?

The CAP file extension is used by some packet sniffing programs as a packet capture file. It holds raw data collected by the program so that it can be analyzed at a later time or with a different program.

Other CAP files could be Construct game development files. These are project files for DirectX games created with the Construct game editing software. They can contain sounds, graphics, models, and other things used by the game.

This extension is also related to ASUS motherboards as the file used when updating BIOS. It's also related to a subtitle/caption file format that stores text meant to be played along with a video; this kind of file is used by some broadcasting companies and might be called a Videotron Lambda file.

Illustration of a person opening a CAP file
Lifewire / Adrian Mangel

CAP is also short for a long list of tech-related terms, but none of them are related to the file formats described on this page. A few examples include computer aided painting, common application platform, cloud access point, and Canon advanced printing.

How to Open a CAP File

There are several ways to use the file, depending on the format it's in:

  • Use Wireshark to open packet capture files. Although we don't have download links for them, some other applications that work include NetScout's Sniffer Analysis and Klos PacketView Pro.
  • Construct is probably your best bet if it's a game-related file.
  • ASUS BIOS update files are used to update the BIOS on ASUS motherboards.
  • Experiments created by Capstone use this extension.
  • Some versions of Capella can be used to open CAP files that are musical scores. The free Capella Reader might support the format, too.

You might be able to use Notepad or a different free text editor to open the file. Many files are text-only files, meaning no matter the file extension, a text editor may be able to properly display the file's contents. This may or may not be the case with your specific CAP file, but it's worth a try if the above suggestions haven't been helpful.

Considering the various types of CAP files there are, and that several programs might be involved depending on the actual format being used in the file, you may find that the program Windows tries to use to open it isn't the one you'd like. See our guide on changing which program opens by default when you double-click a file for help fixing that problem.

How to Convert a CAP File

You can convert a packet capture file to HCCAPX with hashcat.

Use Wireshark to save it to CSV, TXT, PSML, PDML, JSON, or C. You have to first open the file through the File > Open menu, and then go to File > Export Packet Dissections to choose an output format.

There's no reason to convert a Construct file or a BIOS file to another format.

Subtitles ending in this file extension can be converted to TXT, PAC, STL, SCR, and other file formats, using the subtitling program mentioned above.

Still Can't Open It?

If the file openers and converters listed above aren't helpful, double-check the file extension. There's a good chance you're misreading it. Several files use a similar extension to this one, even though the formats are unrelated.

CPA is one example. Although all the same letters are used, that extension is reserved for CADSTAR CAD files. CPAA is similar in spelling, but is what Adobe Captivate appends to the end of shared action files. CAPT, CAT, and CAPX could also easily be confused for a CAP file.

Frequently Asked Questions

  • How do you install a CAP file? To install a CAP file for a BIOS update, first copy the CAP file to a formatted USB flash drive. You can then use the ASUS EZ Flash utility (built into the ASUS BIOS firmware) to load the BIOS update.
  • How do I open a CAP file in Ubuntu? Open your terminal and type locate *.cap to find all CAP files, and then download a file opener such as Wireshark to open the file.
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