FizzyTools Age calculator uses these open-source components. Thank you to their authors.

- Svelte (MIT)                       https://github.com/sveltejs/svelte
- Bricolage Grotesque, DM Sans (SIL OFL 1.1) /age-calculator/fonts/

The date arithmetic is our own code. Day numbers follow Howard Hinnant's public-domain date algorithms
(http://howardhinnant.github.io/date_algorithms.html); the month rule is the one in the ECMAScript Temporal standard.