The probability of an n-gram or word tells you how important a word is to a document. Unfortunately, since a document almost always has important words inter-mingled with conjunctions and determiners and other types of noise, using the raw probabilities may
N-Gram and Word Counter API
The NGramCounter API generates word and n-grams counts based on large amounts of text provided with the desired n-gram size in any language. You can count frequencies of words (unigrams), bi-grams, tri-grams and etc.