Recently I launched ZOMDir's Page inspector. This tool gives insight in the structure and the 'hidden' content of any web page.
When I tested it on the many subdomains of ZOMDir, I discovered that there was room for improvement in the JSON-LD code used.
It was a small change in de code, hence I updated, by hand, the JSON-LD code and without any checks I published the code.
Oops ... a few days later Google mailed me ...
Unparsable structured data issues detected on https://rustyresults.zomdir.
To the owner of https://rustyresults.zomdir.
Search Console has identified that your site is affected by 1 Unparsable structured data issues:
Top Errors
Errors can prevent your page or feature from appearing in Search results. The following errors were found on your site:
We recommend that you fix these issues when possible to enable the best experience and coverage in Google Search.
So I checked the code with ZOMDir's Page inspector and indeed there was an error. However the error given was much more detailed.
ZOMDir's Page inspector stated that there was an
Unexpected token / in JSON at position 554
and showed the JSON code.
Handy. In a few seconds the bug was fixed and checked :-)