An exciting change landed in the development version of Prometheus recently, making PromQL arithmetic expressions in time durations a standard feature instead of an experimental one. For me, duration arithmetic expressions by themselves aren't the truly interesting part. What's really exciting is that as part of this change, Prometheus has added some new PromQL functions, especially step() .

(Although step() is gated behind an 'experimental PromQL functions' feature flag today, it will be made available as a standard function as part of duration expressions becoming a standard feature.)

For people who are familiar with Grafana, step() is the PromQL version of Grafana's $__interval interpolation variable. When you're in a range query, step() is how big the range step is, which was previously unavailable in PromQL even though Prometheus obviously knew this information. Prometheus has also added range() , which gives you the full size of the range duration (and the *_of () functions for further selection if, for example, the step() might be too small). Since PromQL now allows arithmetic expressions in durations, you can use step() in them, allowing you to write PromQL expressions like ' rate(your_metric[step()]) ', where the duration will automatically adjust to whatever the range step is.

Where step() is especially handy for me is when I'm doing ad-hoc graphs directly in Prometheus's web query interface (instead of wrestling with Grafana Explore). Previously I had to go through various increasingly elaborate processes to find out what the step value was for a given time range, so I could plug it into rate() or various *_over_time() things or the like. Now I can just ask for ' rate(...[step()]) ' and it will all work out right, and it will keep working right as I zoom the time scale in or out.

In theory one could replace various Grafana uses of $__interval in PromQL queries with step() . In practice this probably isn't worth it, unless you're running into problems with $__interval for some reason or maybe when you're writing completely new queries for new dashboards and so on. The minor advantage of using step() even in Grafana is that you can easily copy the query out of Grafana and put it directly into Prometheus or a query tool to see exactly what you're getting.

To use step() and friends in Prometheus 3.13, you need to enable some feature flags. But since this is going to be in the next version of Prometheus (unless something goes wrong and the Prometheus developers have to back out this change), I think it's pretty safe to turn on the necessary feature flags and start using step() and friends now, at least in ad-hoc poking around. Even if you have to stop using step() later, it will improve your experience today.

(This elaborates on a Fediverse post of mine .)