Cache validators
ETag and Last-Modified values identify the version or modification time of a representation.
How it works
Strong ETags describe byte identity, weak ETags describe semantic equivalence, and modification dates provide a coarser time-based validator.
How to validate it
Derive validators from the actual representation or a versioned content build and test them across compressed and uncompressed variants.
Common failure
Using deployment time as Last-Modified for every page makes untouched content look freshly changed and wastes recrawl attention.
Machine-readable editions
The same article is available as Markdown and JSON. These alternates are linked here but are not submitted through the sitemap or IndexNow.