ISR and cache invalidation that actually invalidates

Static generation is the easy half. The half that goes wrong is invalidation: an editor publishes, the page does not change, and everyone loses faith in the CMS within a week.

#Tag at three levels, not one

A single global tag rebuilds the world on every keystroke-sized edit. A tag per document leaves index pages stale forever. You want both, plus the type in between.

const tags = ["sanity", body._type];
if (body.slug) tags.push(`${body._type}:${body.slug}`);

for (const tag of tags) {
  revalidateTag(tag, { expire: 0 });
}

Then every read declares which tags it depends on. A doc page tags doc and doc:<slug>; a collection page tags doc only, so publishing any doc refreshes the listing without touching the other doc pages.

#The webhook projection matters

Sanity sends whatever projection you configure. Ask for exactly the two fields the route needs and nothing else — a fat payload is a signature-verification failure waiting to happen on a large document.

{_type, "slug": slug.current}

_type in [
  "post", "caseStudy", "doc", "docCollection",
  "category", "tag", "page", "author", "siteSettings", "docsSettings"
]

# Should return 401 — proves the signature check is live.
curl -X POST https://example.com/api/revalidate \
  -H 'content-type: application/json' \
  -d '{"_type":"doc","slug":"anything"}'

# Liveness, no side effects.
curl -s https://example.com/api/revalidate | jq

#Proving it works

1. Note the current age header: curl -sI https://example.com/docs/... | grep -i age.
2. Publish a trivial edit in Studio.
3. Poll the same URL. age should reset within a few seconds.
4. If it does not, check the webhook delivery log in sanity.io/manage — the failure is almost always a secret mismatch.