1- Grammarly
Grammarly checks your spelling and grammar across different platforms on the web including your Gmail, Facebook, Twitter, LinkedIn etc. It can also ‘fix hundreds of complex grammatical errors, including subject-verb agreement, article use, and modifier placement, to name just a few.’ Grammarly premium offers more advanced features that include:vocabulary enhancement suggestions, plagiarism detection, citation suggestions, and many more.
2- Grammar and Spelling Checker
Another good Chrome extension to check your spelling and contextual grammar. It analyses sentence structure and grammar for possible syntactic errors. It also provides you with suggestions to rephrase and reword your writing and to enhance your style. Its translation functionality allows you to translate your text between 400 languages, access various synonyms and definitions, and several other features.
3- Language Tool
‘With this extension you can check text with the free style and grammar checker LanguageTool. LanguageTool finds many errors that a simple spell checker cannot detect, like mixing up there/their, a/an, or repeating a word, and it can detect some grammar problems. It supports more than 25 languages, including English, Spanish, French, German, Polish, and Russian.’