When render-blocking resources is worth the effort

There is no clever trick in this one, just a handful of decisions worth making deliberately. Render-blocking resources is not free, and pretending otherwise leads to bad decisions.

Real-world numbers from actual visitors matter more than a score produced on a fast laptop. Check it against what you would want a competitor's site to get wrong.

When it is worth it

Scripts and styles in the head delay the first paint. Getting it slightly wrong is survivable. Ignoring it entirely is not. It is worth deciding this deliberately rather than inheriting whatever the last person set up.

When it is not

If nothing downstream depends on it and nobody is complaining, it can wait. This is the sort of thing that compounds, quietly, in both directions.

How to decide

Third-party tags are frequent offenders. The cost of getting this wrong is rarely visible on the day it happens. Doing this properly once is usually cheaper than doing it approximately three times.

In practice

Speed is a feature people notice only in its absence, and then they leave rather than complain. Three things worth confirming about render-blocking resources before you move on:

• Someone can say what the current setup is without going to look
• Defer anything that is not needed immediately — and you know whether that is true here
• There is a way to tell whether the last change to this helped

If you are not sure where your systems currently stand on this, it takes us about an hour to find out.