{
  "schemaVersion": "crawler-atlas-1",
  "atlasVersion": "atlas-2026-07-28-v1",
  "canonical": "/atlas/cache-validators",
  "title": "Cache validators",
  "category": {
    "slug": "http",
    "title": "HTTP behavior and efficiency"
  },
  "definition": "ETag and Last-Modified values identify the version or modification time of a representation.",
  "mechanism": "Strong ETags describe byte identity, weak ETags describe semantic equivalence, and modification dates provide a coarser time-based validator.",
  "validation": "Derive validators from the actual representation or a versioned content build and test them across compressed and uncompressed variants.",
  "commonFailure": "Using deployment time as Last-Modified for every page makes untouched content look freshly changed and wastes recrawl attention.",
  "related": [
    "/atlas/conditional-requests",
    "/atlas/compression"
  ],
  "modified": "2026-07-28"
}