Mobile performance: what to get right first

Teams tend to reach for this after something has already gone wrong. If you only fix one thing about mobile performance this quarter, make it the first item below.

Performance work is mostly subtraction, which makes it unpopular and effective. The failure mode is not doing it wrong, it is doing it once and assuming it stays done.

Start here

Phones have less processing power and worse networks. That sounds obvious written down. It is still the thing most often skipped. The teams that stay on top of it are the ones who put it on a calendar rather than a wish list.

Then this

Test on mid-range devices, not just the newest. The teams that handle this well are rarely the ones with the biggest budgets. The teams that stay on top of it are the ones who put it on a calendar rather than a wish list.

Eventually

JavaScript costs far more on mobile than on desktop. There is a version of this that is over-engineered, and it is worth avoiding. The teams that stay on top of it are the ones who put it on a calendar rather than a wish list.

The short version

Real-world numbers from actual visitors matter more than a score produced on a fast laptop. Three things worth confirming about mobile performance before you move on:

• Someone can say what the current setup is without going to look
• JavaScript costs far more on mobile than on desktop — and you know whether that is true here
• There is a way to tell whether the last change to this helped

If any of that sounds like a description of your current setup, it is fixable.