Why it shows up in your week
Core Web Vitals turn page speed from a vague complaint into three metrics the team can measure before a launch damages traffic or conversion.
In plain language
Good thresholds at the 75th percentile: LCP ≤2.5s, INP ≤200ms, CLS ≤0.1. Needs improvement and poor bands sit above those cuts. Field data (CrUX/RUM) beats a single lab run on a fast laptop.
LCP is when the main content appears. INP is how fast the page responds to clicks and taps. CLS is whether the layout jumps under the user’s thumb.
Money templates (home, pricing, campaign landers, checkout) deserve budgets in release checks, not only in an annual audit.
A green Lighthouse screenshot on office Wi-Fi can still hide failed mobile field data. Believe the users’ phones.
Facts worth keeping
Last reviewed
- Type
- Google user-experience metrics (ranking-relevant)
- Also known as
- CWV
- Metrics
- LCP (load), INP (responsiveness), CLS (stability)
- Good LCP
- ≤2.5s at the 75th percentile
- Good INP
- ≤200ms at the 75th percentile
- Good CLS
- ≤0.1 at the 75th percentile
- Prefer
- Field data (CrUX / RUM) over a single lab run
Not the same as
- A single Lighthouse scoreLab tools help debug. Field data decides whether real users are fine.
- TTFB aloneTTFB influences LCP but is not a Core Web Vital. You still need LCP, INP, and CLS.
Where it bites
Core Web Vitals bite during paid campaigns, SEO pushes, and relaunches.
If performance is measured only after launch, the team finds the regression after users and crawlers already felt it.
What to check
- Which URL templates fail LCP, INP, or CLS on mobile field data?
- Is the LCP element prioritised, sized, and served in the right format?
- Which scripts, embeds, or rendering work block interaction during real user sessions?
- Do campaign landers share the same performance budget as the homepage?
- Is there a release check that catches regressions before go-live?
Common questions
What are Core Web Vitals?
Core Web Vitals are Google metrics that measure loading speed, responsiveness, and visual stability through LCP, INP, and CLS.
What are the good Core Web Vitals thresholds?
At the 75th percentile of real users: LCP at or below 2.5 seconds, INP at or below 200 milliseconds, and CLS at or below 0.1.
What should you check first for Core Web Vitals?
Start with mobile field data, the LCP element, third-party scripts, image delivery, layout stability, and whether the slow templates match valuable SEO or conversion pages.
Do Core Web Vitals affect SEO?
Yes. Google uses them as a page experience signal, and they often correlate with conversion because slow or unstable pages make tasks harder.
Lab or field data?
Use both. Field data tells you if users are fine. Lab traces explain why a template fails.