Simply feed it a .swf file and it will spit out the equivalent HTML5 as a JSON file.
While Google says that full Flash-based games won’t work with the converter just yet, vector graphics, embedded fonts, images and timeline animations should work fine. Google has set up a gallery of example conversions and it’s fair to say that they make the leap to HTML5 well.
While Google isn’t promoting Swiffy as anything more than an experimental tool at the moment, the tactical advantage for Google of being able to get people away from proprietary formats to its beloved open standards mean that further developments to this converter seem highly likely. As a side effect, Flash-averse Apple should be pretty pleased about this too.