{
  "slug": "cwv-weakest-vital",
  "name": "Weakest vital",
  "aliases": [
    "Worst vital per page"
  ],
  "definition": "For each of the slowest-rendering pages, which of the three Core Web Vitals is graded worst.",
  "category": "Page experience",
  "type": "derived metric",
  "unit": "the name of one vital, or none when no vital has a value",
  "direction": "neutral",
  "verification": "verified",
  "calculation": "Among rendering time, layout shift and responsiveness, each vital with a numeric value on the page is graded and the worst grade wins, with ties resolved by the order the vitals are checked. Deliberately chosen by GRADE severity, not by the smallest number, because the three vitals sit on scales orders of magnitude apart and a raw minimum would always pick layout shift.",
  "aggregation": "Computed per page, on the up-to-ten SLOWEST-RENDERING pages. The page rows are read sorted by descending rendering time, rows with no rendering time are dropped before the ranking, and the top ten of what remains are kept.",
  "grain": "One vital name per listed page.",
  "dimensions": [
    "page"
  ],
  "requiredFilters": [
    "date_range"
  ],
  "sources": [
    "lighthouse"
  ],
  "reports": [
    "core-web-vitals-report"
  ],
  "skills": [
    "cwv-regression-watch",
    "technical-health-audit"
  ],
  "verbs": [
    "site_health_cwv_check"
  ],
  "rungs": [
    "R1"
  ],
  "levers": [
    "L1"
  ],
  "questions": [
    "What is the biggest page-experience problem on this page?",
    "Where should engineering start?"
  ],
  "interpretation": "The routing hint on a fix list: it names which vital to open first on a given page. It answers what is worst, not how bad, pair it with that vital's own value and grade before scoping any work. And because the list of pages was chosen on rendering time, it is a fix list for slow pages, not a survey of where the site's page-experience problems are.",
  "caveats": [
    "The selection and the verdict use different vitals. Which PAGES are considered is decided by rendering time alone, the slowest ten, while which VITAL is named on each of them is decided by grade severity across all three. A page whose only failing vital is layout shift or responsiveness will not appear at all unless its rendering time is also among the worst.",
    "The performance score is excluded from the candidates; only the three Core Web Vitals are considered. It does not decide the page ranking either, despite being the score the page-experience verdict is built from.",
    "A page with no rendering time is dropped before the ranking, so absence from the list is not evidence of health.",
    "Ties are broken by check order rather than by magnitude, so two vitals in the same band will always resolve the same way.",
    "It reports severity band, not distance from the threshold: a page barely over the line and one far past it both read the same.",
    "With results split by device the entries are page-by-device observations, so an entry names the worst vital for one device's measurement of that page, not for the page overall."
  ],
  "freshness": "varies by site, priority URLs can run nightly; most pages far less often. The collection date rides on the card rather than being assumed.",
  "failureModes": [
    "Describing the list as the worst-scoring pages, it is the slowest-rendering pages.",
    "Reading the named vital as the largest opportunity rather than the worst band.",
    "Assuming a page absent from the list is healthy when it may simply have no rendering measurement."
  ],
  "notSameAs": [
    {
      "slug": "cwv-vital-grade",
      "why": "The grade tells you which band a named vital is in; the weakest vital tells you which vital is in the worst band on a page. One is a value, the other is a selection."
    }
  ],
  "related": [
    "cwv-vital-grade",
    "cwv-grade-distribution",
    "largest-contentful-paint"
  ],
  "workflows": [],
  "lastVerified": "2026-08-04"
}