This excellent article rewriter tool will thoroughly scan your entire content, looking for the words that it can replace with a synonym. All the words that it replaces with a substitute will be highlighted in the bold and colorful text. By clicking on any of the highlighted words or phrases, you can see the original word, suggestions or add your own word. Also, you can click on the original word to revert or click on any other word to replace.
Other article spinners also require that you enter your own custom synonyms manually or individually approve lists of potential synonyms as they are presented to you. This is another way of expecting you to do most of thinking, as opposed to expecting the software to be smart enough to instantly make judgment calls for you. Thus, one of Spinbot's main goals is to make the article spinning process as quick and painless as possible.
Imo it is not possible for google to detect properly spun content, it is not worth computing power it requires. They can do this using ngrams for example, but it is uses a lot of queries. And for example article spinner I coded beats this algo, so google cant detect that the content is spun. Manual spinning is also good but it takes more than 30 minutes per article.