What is a .cap file?
A .cap file is a network packet capture. Its registered MIME type is application/vnd.tcpdump.pcap, which places it in the application or document family of formats.
CAP is a binary format: the contents are not readable text, so opening it in a text editor shows scrambled characters.
Files of this type usually begin with the bytes A1 B2 C3 D4. That signature is how programs recognise the format even when the extension is wrong or missing.
The same format is also saved with the extensions .dmp, .pcap.
CAP file format details
| Extension | .cap |
|---|---|
| Format | Network packet capture |
| MIME type | application/vnd.tcpdump.pcap, application/x-pcap, application/pcap |
| Category | Application or document |
| Text or binary | Binary |
| File signature | A1 B2 C3 D4 |
| Registered with IANA | Yes |
| Other extensions | .dmp, .pcap |
How to open CAP files
| Windows | CAP files (Network packet capture) are made by specific software. The reliable way to open one is with the program that created it; a generic viewer will only show raw data. |
|---|---|
| Mac | The same applies on a Mac: look for a Mac version of the program that makes CAP files. |
| iPhone and iPad | Phones rarely open this type of file directly. The viewer above can show what is inside it without installing anything. |
| Android | The same applies on Android. The viewer above shows the first bytes of the file so you can confirm what it is. |
Can you convert a .cap file?
TapToConvert does not convert CAP files. The usual route is to open the file in the program that made it and use its Export or Save as option.
CAP file FAQ
What is a .cap file?
A .cap file is a network packet capture, with the MIME type application/vnd.tcpdump.pcap.
How do I open a .cap file?
With the program that created it. The viewer on this page shows what is inside without installing anything.
Is a .cap file safe to open?
CAP files hold data rather than programs, but any file from an unknown source can be crafted to exploit the software that opens it. Keep that software up to date. The viewer on this page only reads the bytes and never runs anything.
What is the MIME type of .cap?
application/vnd.tcpdump.pcap, and it is also seen as application/x-pcap or application/pcap. Web servers send this type so browsers know how to handle the file.
Is CAP a text or binary format?
Binary. Its contents are not readable as text.
File type facts come from the IANA media type registry, the mime-db project and the freedesktop.org shared MIME database.