As with phrase structure-based parsing, the evaluation of dependency parsers proceeds by measuring how well they work on a test set. An obvious metric would be exact match (EM) — how many sentences are parsed correctly; however, most of the times this metric is too pessimistic. Alternative methods are:

• Labelled attachment score (LAS), which looks at the proper assignment of a word to its head along with the correct dependency relation.
• Unlabelled attachment score (UAS), which looks at the correctness of the assigned head, ignoring the dependency relation.
• Label accuracy score (LS), which looks at tokens with correct labels, ignoring where the relations are coming from.