Copy and paste your essay below, then click on or double-click on the textbox. All of your to be verbs should highlight in a red color and bolded font. If it highlights a contraction that doesn't look like a to be verb, then it's more than likely a contraction for one (e.g., it's means it is). Once all the verbs are highlighted, you can single click to select the red words and fix your verbs (if you choose to edit in the box below).
Note: It doesn't know the difference between nouns and verbs, so if you're talking about how something is in the state of being (as in the noun), it'll still be highlighted. The same applies to certain contractions. For example, "he's" can mean "he has," or "he is."