Astro 6 — static-first sites, islands, content collections

The prime directive

Ship zero client JavaScript by default. Hydrate the smallest possible surface, as late as you can get away with. An .astro component renders to HTML at build time and ships no runtime; every island is a bundle the visitor downloads, parses, and executes. Content and marketing sites win on TTFB/LCP and Lighthouse, not on React-everywhere. If you find yourself adding client:load to make a page "work," stop — the page already works; you are adding interactivity, and interactivity is the expensive exception, not the default.

First: detect the project version

Astro 6.0 is stable (released 2026-03-10); the Astro 5 line is still production-ready. Do not mix advice across majors — read package.json → the astro version before advising. What v6 changes, per the upgrade-to-v6 guide: