Google Webmaster Tools is a software package that allows website developers to check indexing status of websites within the Google search engine and is used in optimisation for checking the visibility and performance.
Google are openly reporting that the Webmaster Tool bug may falsely report a sharp decline in indexed pages and website performance.
Webmasters and marketers have noted a bug in the new “Google Search Console” (Webmaster Tools) that shows huge declines in the number of indexed pages displayed in its Google sitemaps reports.
Don’t worry this is not just your site – there has been a noticeable decline in in reported traffic and globally hundreds of thousands of websites have been affected since early July 2015.
Google is actively working on a fix for the bug, so no need to panic if you have seen a recent decline in your index count in this month.
It is just a Google reporting glitch and does not affect your traffic or rankings within Google.