A short guide to mobile performance

Teams tend to reach for this after something has already gone wrong. Everything we would tell a client about mobile performance in the time it takes to drink a coffee.

Speed is a feature people notice only in its absence, and then they leave rather than complain. It rarely shows up as a line item, which is exactly why it slips.

Why it matters

Phones have less processing power and worse networks. There is a version of this that is over-engineered, and it is worth avoiding. The practical test is whether someone new to the project could tell, in a minute, that it had been handled.

The practical version

Test on mid-range devices, not just the newest. There is a version of this that is over-engineered, and it is worth avoiding. If it only works because one person remembers to do something, it does not work yet.

Where it usually goes wrong

JavaScript costs far more on mobile than on desktop. There is a version of this that is over-engineered, and it is worth avoiding. Assume whoever inherits this will have half your context and none of your patience.

How to tell if yours is fine

Performance work is mostly subtraction, which makes it unpopular and effective. Three things worth confirming about mobile performance before you move on:

• Someone can say what the current setup is without going to look
• Phones have less processing power and worse networks — and you know whether that is true here
• There is a way to tell whether the last change to this helped

The point is not perfection, it is knowing which of these you have consciously chosen to skip.