Image
What is a .cap file?
A .cap file is a Microsoft Network Monitor Packet Capture (version 1). This is an image format — a picture, drawing or graphic. Confusingly, this extension has been used by 4 different formats over the years — they're all listed below.
This extension has been used by more than one format
4 different formats have claimed .cap over the years, so two files with the same extension aren't necessarily the same kind of thing.
How to open a .cap file
- GIMP (free) and IrfanView open a very wide range of image formats, including obsolete ones.
- XnView MP is the best bet for unusual or legacy image types.
- Your operating system's built-in viewer may work for mainstream formats.
The registry records this extension against Microsoft Network Monitor Packet Capture, Microsoft Network Monitor Packet Capture, pcap Packet Capture and others, so software from that family is the most likely match.
How to convert a .cap file
- Open it in GIMP or XnView and export as .png (lossless) or .jpg (smaller).
MIME type
When a .cap file travels over the web, servers label it with this MIME type:
application/vnd.tcpdump.pcapThe technical record
For archivists, developers and the merely curious: these are the PRONOM registry entries for .cap.
| Format name | Version | MIME type | PUID |
|---|---|---|---|
| Microsoft Network Monitor Packet Capture | 1 | — | fmt/777 |
| Microsoft Network Monitor Packet Capture | 2 | — | fmt/778 |
| pcap Packet Capture | — | application/vnd.tcpdump.pcap | fmt/779 |
| Phase One Raw Image | — | — | fmt/1060 |