The two-span bar
A track span with a background, a fill span with a width. Accessible for free (the number is text beside it), themeable for free (tokens), and impossible to make interactively confusing. Every distribution on /quality and every run bar on the prompt pages is this, and none of them mislead.
When you need more
Axes, brushing, log scales, live streaming — that is chart-library territory, and pretending otherwise is how hand-rolled SVGs get hover bugs. The honest line: CSS bars for counts and proportions; a library when the reader must explore, not just read.
One rule even the CSS version must keep: the visual is decoration, the number is the data. A screen reader should get the same truth without the bar.
<span class="track">
<span class="fill" style="width: 72%"></span>
</span>
<span class="value">72 / 100</span>