Paul Irish showed off a cool new feature of the Chrome DevTools called Canvas Introspection in a talk at EdgeConf.
To try it out on your own
<canvas> projects, you first need to install Chrome Canary. Canary is a bleeding-edge version of Chrome that you can run alongside your more modest stable or beta version. After you download it, open it up and visit
chrome://flags and enable the DevTools Experiments:
Now restart Canary and open up DevTools and hit the little gear icon in the lower right to open up the DevTools settings:
You should now see an "Experiments" tab in the left sidebar and the option to turn on "Canvas Inspection":
Make sure to watch Paul's talk for the cool things you can do with it.