Fathom can be implemented in a browser, in extensions and even server-side software. It is a dataflow language like Prolog.
Mozilla’s developers have designed Fathom to calculate DOM nodes based on user-specified conditions, annotations and a system of types. This process helps the framework to extract meaning from parts like address forms, previous/ next buttons and textual content found on the website.
According to Mozilla’s senior staff software architect, Erik Rose, the framework is still in the early stage of development. It nevertheless enables the browser to identify meaningful parts on a page and show the summary.