How I monitor Core Web Vitals without a vendor
A free, honest setup for watching the metrics that move your search rankings.
You do not need a paid real-user-monitoring vendor to keep Core Web Vitals honest. You need a little discipline and a free dataset most publishers already have access to.
The free stack
My setup has two parts. The CrUX dataset gives you real-world field data for your own domain at no cost. A small field-data script, using the standard web-vitals library, fills in the page-level detail CrUX aggregates away.
What to actually measure
Three metrics, watched in the field rather than the lab:
- LCP — almost always the one a publisher fails first.
- CLS — the one ad layouts quietly destroy.
- INP — the metric most teams are still not watching closely enough.
Lab scores are a rehearsal. Field data is the performance the audience actually attended.
The one thing to watch
Watch the 75th percentile, not the average. Google evaluates the experience at the 75th percentile, so an average that looks fine can hide a real ranking problem. If you optimise for the mean, you are optimising for a number nobody is graded on.
Why bother doing it yourself
A vendor will package this more nicely, and one day you may want that. But owning the measurement keeps you honest about your own ad stack, because the script will happily show you that your own ads are the regression. A vendor dashboard is easier to look away from.