Fiddler supports the following formats by default:
HTTP Archive JSON
HTTP Archive XML
These files are exported from the IE9 Developer Tools Network Tab.
HTTP Archive JSON v1.1 (*.har)
This format does not support storage of non-textual response bodies.
HTTP Archive JSON v1.2 (*.har)
This format supports storage of non-textual response bodies. Because these .har files are not compressed, Fiddler will only store non-textual content smaller than 32kb by default. This limit can be increased by setting a Fiddler Preference:
Visual Studio Web Test XML
WCAT Load Test Script
The Raw Files export format allows you to easily dump captured response files to a folder on disk. This allows you to easily collect (for example) audio, video, or image files.
HTML5 AppCache Manifests
Beyond these default formats, developers can create their own Import and Export classes by implementing the ISessionImporter and ISessionExporter interfaces using any .NET language. There is no particular requirement that the classes store data in a file. You could build a class that saves or loads traffic from a local database or a data store in the cloud.