These are online style checkers. They are feedback tools which identify some of the common sentence-level grammatical errors as well as spelling errors. Keep in mind no online style checker is perfect and you will get some false positives–so do not take their advice blindly. However, they can be quite helpful. All have free versions.
Free service from Proz.com. You can upload a PDF, DOCX, DOC or TXT file (maximum file size is 100 MB); for best results use DOCX.
Click on the “Write” button (top left-hand corner of the page), then clear the sample by clicking somewhere in the sample text, press CTRL+a to highlight all the text, and hit the delete key to delete. Next, type in, or pate, the text you want to check. Click on the “Edit” button when you are finished.
Nitpicker: an overly picky language style checker
Click on “Enter your text” to input the text you want checked. When finished, press the Analyze button.
ProWritingAid: Improve you writing
The online check is free; however, the Word, Google Docs, and other plugins are not.
The Writer’s Diet
Can check 100 to 1,000 words at a time.