Have a look at ‘Vocabulary Profiling 1‘ for reasons to profile vocabulary.
One of these gives you the Type-Token Ratio (TTR) of your text. This is the number of word types against the number of word tokens. If you have the word ‘the’ 12 times in a text, that’s 12 tokens, but 1 type. The TTR indicates lexical variation (the higher the number, the more varied the vocabulary). When I did my first degree we had to count each word and each type and calculate this ourselves (I like LexTutor!).
Another feature LexTutor offers is calculating the Lexical Density of a text. This is the number of content words as opposed to function words in a text. The higher the Lexical Density, the more complex the language.
LexTutor also allows you to check your text against different corpora than VocabKitchen. As well as the Academic Word List (AWL), you can check against the BNC-COCA (which is similar to the CEFR in VocabKitchen).