A web font decides two things a visitor notices: whether text is visible while the file is still loading, and to whom the browser connects before anyone has agreed to anything. Both are settled in the @font-face rule and in the preload line above it. This check reads the page and its stylesheets, collects every rule and asks each font file for its headers alone.
From this server: one request for the page, up to four for stylesheets, and one HEAD per font file. The font files themselves are never downloaded. No cookies are sent, no scripts are executed, nothing is stored beyond the rate counter.
Limits worth knowing: only stylesheets linked in the served HTML are followed, at most four of them and 512 KB each. Rules that a script adds later stay invisible, and a font declared in CSS but never applied to any element is still counted here.