What are the tools to find duplicate content on website?

Duplicate content is content that appears on more than one online location, meaning different websites. If you publish your own content in more than one place, you have duplicate content. If you copy someone else’s content onto your site or if they publish yours on their site, that’s duplicate content.
It’s always a good idea to double check everything you write using plagiarism checkers to make sure your content is viewed as unique. Several of these tools are available at no cost.

1. Copyscape:  With this tool you can quickly check the content that you have written against already published content in a matter of seconds. The comparison tool will highlight content that shows up as duplicate, and it will let you know what percentage of your content matches already published content.
2. Plagspotter: This tool can identify duplicate pages of content across the web. It’s a great tool for finding plagiarists who have stolen your content. 
3. Duplichecker: This tool quickly checks the originality of the content you are planning to post on your site. Registered users can do up to 50 searches per day.