Do people design UIs first?

I just basically define what I need in a UI in plain text

when the prototype is built.

I extract the repeating units, then add design to it.

If you're product first, you design the UX, which includes the UI.

If you're tech first, you do what you do.

It depends on what you’re doing. If you’re working on a product like Slack, for example, the right question will often be not what UI your feature needs but what feature your UX idea needs.