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Astro 5.17: an SSR upgrade checklist for cookies, loaders, and images

Astro 5.17 expands configuration across cookies, content loaders, and image optimization, plus a new project-wide default for dev toolbar placement. The changes target common production and embedded-app edge cases without requiring custom workarounds.

Astro 5.17 adds new configuration hooks for SSR apps, content loading, and image processing.

Key facts

  • Astro.cookies.set() now supports partitioned: true for embedded/iframe scenarios; partitioned cookies require secure: true and are commonly paired with sameSite: 'none'.
  • The dev toolbar supports a project-wide default placement via devToolbar.placement, while still allowing per-developer overrides from the toolbar UI.
  • The file() content loader’s parser() can be async, enabling awaited enrichment steps while building a collection’s final data.
  • The glob() loader adds retainBody: false, letting projects skip storing each entry’s raw body alongside rendered output to reduce the deployed content data store size.
  • astro:assets image transforms support a background color when converting from transparent formats (like PNG) to formats without alpha (like JPEG), using standard CSS color syntax.