Google announced the launch of a new tool to help novice webmasters create rich snippet markup (structured data) for their web pages. The tool is a point-and-click tool that lets a webmaster click on words or phrases and add elements of structure data to it without having to go into the code and add it to the HTML.

Here is how Google describes it:

It looks easy, I have not tried it because of a couple reasons:

(1) I have HTML based structured data markup on most of my sites that need it.

(2) It is only available right now for event based data.

That being said, someone asked, what if you have both HTML markup and then also use this tool to add markup. What does Google decide to use?

John Mueller answered this on Google+ saying:

The best case, someone should try to test it and see what Google decides to use. Let us know.

Forum discussion at Google+ and Google Webmaster Help.