These services correct all types of mistakes in a text. Common mistakes are,
For every person having difficulty with the English language has the biggest problem with grammar – as described in a great blog post here; http://www.sentencechecker.info/professional-sentence-fragment-checker/. The online sentence checker has made it easier. One such online service called the Ginger has a great way of not just correcting your mistakes in a sentence, they also highlight the errors so that you can also see your own mistakes. In this way, you can learn from your mistakes and avoid making them again in the future.