har
From AlertFox Website Monitoring
The file extension har is used by the HAR Viewer (HTTP Archive Viewer). It is an online tool visualizing HTTP Archive (HAR) files produced by HTTP tracking tools. These files contain a log of HTTP client/server conversation and can be used for an additional analysis of e.g. page load performance.
See http://wiki.alertfox.com/file_extension_har
Source: http://www.softwareishard.com/blog/har-12-spec/
