sp_Blitz is a stored procedure that checks the health of your Microsoft SQL Server instance.
sp_Blitz is a free health check stored procedure for Microsoft SQL Server. It reviews your SQL Server's dynamic management views, error logs, and configurations, and gives you a prioritized list of things you want to be aware of before you work on that server.
It's designed for accidental database administrators - people who are responsible for the uptime and speed of their database servers, but don't have a lot of in-depth professional training for SQL Server. Each line has a URL you can copy/paste into your browser for more details about that warning. If you have a question about the warning, start with that URL first before asking questions here.
The sp-blitz tag is for support with the script. If you have a question about a particular SQL Server feature or error, and you happen to find it by using sp-blitz, you don't have to use this tag. (sp_Blitz surfaces all kinds of SQL Server nastiness.)
There are separate tags for sp_BlitzIndex, sp_BlitzCache, and the other free stored procs from the same company.