Great writeup! Your journey perfectly captures the universal developer dilemma: "Never roll your own X... until you absolutely must."

The bundle size reductions are impressive (230kB client-side savings!), and your RFC 9557 alignment is a smart forward-looking move. Two questions:

Edge cases: How does your parser handle leap seconds or pre-1582 Julian dates? (e.g., astronomical data) Temporal readiness: Will @11ty/parse-date-strings become a temporary polyfill until Temporal API stabilizes, or a long-term solution? Minor observation: Your comparison table shows Luxon supports YYYY-MM-DD HH (space separator) while RFC 9557 doesn’t – this might break existing Eleventy setups using space-delimited dates. Maybe worth an explicit migration note?

Regardless, fantastic work balancing pragmatism and standards. The web needs more focused libraries like this!