Red underlines mean that Grammarly has spotted a mistake in your writing. You'll sea one if you mispell something. (See what we did there?) You'll also see an underline, if you misuse a punctuation mark.If you're worry about typos or grammatical errors that could effect your credibility, Grammarly will helps you fix those to. Click any of Grammarly's suggested corrections to apply them to your text, or open a brief explanation to learn more about error and how to fix it. But there's more to good writing than speling, punctuation and grammar. (Sorry, couldn't resist.) Brilliant sentences are clear and concise. Underlines that are blue indicate that Grammarly has spotted a sentence that is unnecessarily wordy. Grammarly scores each text based on how clear it will be to your readers and gives you guidance in order to do a revision of it in an effortless manner. Afterall, there are some sentences that are gramatically correct but still awkward and hard to follow. It goes without saying that sometimes you can actually improve a sentence by completely eliminating words that are basically unnecessary.