I have been using Sonarwhal to check my website for errors for quite a while. This is quite a useful tool to get your website checked for best practises and errors.
So far, I have managed to clear out many issues raised by the online scanner provided free-of-charge. The downside of the scanner right now, is that I cannot set rules. Like I can't ignore certain domains that are not under my control, thus it reports their errors. The other downside I face is also a timeout between scans. I like to scan each time I make a site modification, which can be seconds apart. You can install this tool on your local premise to overcome these limitations.