Type is the interface

Ask someone why a page feels trustworthy and they will point at almost anything except the type. The logo, maybe. The photography. Meanwhile the reason is sitting in front of them, doing its work silently, in fourteen or sixteen pixels.

Most text is read, not looked at

This sounds obvious and is routinely forgotten. A typeface chosen for a headline screenshot will be lived in for hours by someone reading documentation at eleven at night. Choose for the paragraph first and the poster second.

That means testing at real lengths. Not a line of placeholder, but four hundred words of the actual thing someone will read, at the actual width, on the actual screen. Problems that are invisible in a heading become obvious in the fifth paragraph.

Measure, leading, contrast

Three numbers carry most of the weight. Line length between roughly forty-five and seventy-five characters. Line height a little looser than feels necessary, especially for longer text. And enough contrast that a tired reader on a bright train is not squinting.

Get those right and an ordinary system font will read beautifully. Get them wrong and no amount of licensing money will save you.

One family, used properly

The instinct to pair two or three faces usually comes from boredom rather than need. A single well-drawn family with a real range of weights will carry an entire product, and it will hold together in places you never designed for: an error state, an email receipt, a dense table on a small phone.

Add a second face when you have a reason you can say out loud. Not before.