The SRx Core contains a suite of tests to aid with troubleshooting a SharePoint 2013 and 2016 on-premises search farm. This package surfaces complex diagnostics in standardized PowerShell reports. Operations staff can utilze SRx Core to check for specific instances of search health deficencies.

Watch for blog posts and documentation covering each SRx test and information to run the SRx Core. Also, look for blog posts on the complete SRx which includes a search dashboard and alerts.
  -- Send an email to searchengineers@microsoft.com to be notified of important updates to SRx Core

Key blog posts about this tool:

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Recent updates:

Sample output using New-SRx -RunAllTests   (...to run all of the tests)

And, when things have gone horrbily wrong, a sample detailed output using: New-SRx -RunAllTests -Details  
(...to run all of the tests and display details)

I hope this helps...