This might include profilers, production server monitoring, static analysis tools, etc. They can be language specific or not.
What are you using day-to-day/week-to-week/month-to-month?
Counters to measure
Profilers like pprof to dive deep https://golang.org/pkg/runtime/pprof/
I also use sentry.io to monitory my performance in live environment. Their new "Performance" system allows you to measure and track response times for whole endopoints, and for parts of the endpoints. Quite useful to detect slow queries and so on. Previously in my carreer I have also used newrelic with much success, but it is at least 7 years since I have used that, so can't give a recent experience with them.
Ps. no affiliation to any of the mentioned products/services above.