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Visual studio does a great job of verifying as you type.

Also, don't wait for google to tell you if you have duplicates. That is what I was doing - silly me! I did a comprehensive headline check and I discovered that there were more than a thousand duplicates in our system because back a few years, one of the editors was doubleclicking the mouse when publishing stories and that was before I put in a mechanism to prevent them. I thought there were only occasional ones and I'd fixed them, but it seems I didn't! So check every page on your site for duplicate titles, duplicate descriptions and duplicate content.