PaperRater can help you by guiding you to write better and correct content with a number of free tools it offers. You can run your content through the plagiarism checker tool offered by PaperRater to check for duplication.
It also offers and grammar and spelling checker tools to help you write correct and better content.
The tool is simple to use, all you have to do is to paste your content and run the tool to analyze your content. After the analysis is complete, the tool give you detailed statistics around your content and suggestions to make changes.