Hey this is cool! I tried Shakespeare's Sonnet 29 and it thinks only half the lines have the correct meter---which partly goes to show how flexible real poems can be but also could highlight places your tool could be refined. I think line 1 ends in a spondee. Also in sonnets starting a line with trochee-iamb is so common you might want to accept that as metrical too. Does it use punctuation as hints? In line 6 the comma at "Featured like him," seems important to the rythym.

For the ultimate challenge you should see if you can make any sense of Hopkins. :-)

When I was in Classics grad school I started a metrical search engine project. The idea was to give scholars a search box with a regex-like syntax for finding lines in a corpus matching metrical features. For example you could find all the lines in Homer with feminine endings. With Perseus it's easy to get lots of Greek & Latin texts. Then you just have to scan everything, but you can program that. I had an on-paper program to do dactylic hexameter. If anyone else thinks that might be a helpful tool, let me know. (Also if you work for Thesaurus Linguae Graecae and want to hire me to write this thing, I can make availability! ;-)