There’s no shortage of performance advice, is there? The elephant in the room is the fact that it’s challenging to interpret: Everything comes with caveats and disclaimers, and sometimes one piece of advice can seem to actively contradict another. Phrases like “The DOM is slow” or “Always use CSS animations” make for great headlines, but the truth is often far more nuanced.

Take something like loading time, the most common performance topic by far. It’s rarely consistent. When it comes to other ways to measure performance, you’ve probably seen enough JavaScript benchmarks to last a lifetime. You may have also heard that 60 FPS matters. But when? All the time? Seems unrealistic.

Very few of us have unlimited time to throw at optimization work, far from it, and we need criteria that help us decide what’s important to optimize (and what’s not!). When all is said is done, we want and need clear guidance on what “per formant” means to our users, because that’s who we’re building for.

On the Chrome team, we’ve been thinking about this, and we’ve come up with a model to put the user right back in the middle of the performance story. We call it the RAIL model.