Here’s how it works. You sign up to some fancy editing software (I use ProWritingAid for around $US40) and upload your manuscript. This automatically checks for grammatical errors, overused words, poor sentence connections, long paragraphs, etc. Here is one result – plagiarism – for 3 WISE MEN:
Such analytical processes are actually very helpful but should only be treated as a guide. In many cases (e.g. with foreign place names) the software does a poor job. However, you do need to get past the constant reminders and look at the corrections in context. Do the words and paragraphs still flow? Is the dialogue crisp?
In conclusion, online writing tools like these are fine, but there an “Art to Correction”!