Generation of a semantic diff is described. A machine according to some example embodiments generates first and second parse trees by parsing the first and second documents using a grammar of a coding language common to both documents. The machine classifies subtrees within these parse trees and determines that a first subtree from the first document shares a classification with a second subtree from the second document. Based on their sharing of the classification, the machine selects these two subtrees for comparison to each other and also chooses a comparison procedure based on the shared classification. The machine then executes the selected comparison procedure with the selected two subtrees as input and generates a differential subtree that indicates one or more differences between the two subtrees. The machine may also generate a differential tree that indicates differences between the entireties of the first and second documents.