Google Docs includes a grammar-check function along with its spell-check tool. The grammar-check tool alerts the writer to possible grammatical errors by underlining those words.
The grammar check function works in the same manner as the spell check function. For instance, the word "its" will be underlined if it's possible that the writer used the incorrect form of the word based on the meaning of the entire sentence. The tool will open a dialog box that asks the user what is meant, and displays a list of other possible words, giving the writer the option of changing the original.
Docs is Google's free, web-based office software suite offered as part of the Google Drive service.