A grammar checker is a program often included in word processors and which is supposed to check writing for errors in grammar.
Unlike spellcheckers, which have reached a high level of precision, grammar checkers are still in their infancy and are unlikely to detect any but the most serious mistakes.
In other words, in the sentence below they will probably only detect that what was meant was "in spite of". All the other errors won't be detected.
- Word 2010 issues the following message: "Possible Word Choice Error: off. Suggestion: of."