Core Web Vitals Checker — Grade your page-experience scores

Paste LCP, INP, and CLS from PageSpeed, CrUX, or Microsoft Clarity Performance metrics to see Good, Needs improvement, or Poor. Shows common causes and fixes aligned with Clarity and web.dev. Runs on your device—numbers are not uploaded to a server. Example: 3.2 s / 280 ms / 0.18 → all Needs improvement.

How it works

Enter LCP (seconds or ms), INP in ms, and CLS. The tool maps each value to Good / Needs improvement / Poor and, when not Good, shows causes and fixes summarized from Microsoft Clarity Performance metrics guidance.

Thresholds and rules

Bands follow industry Core Web Vitals (web.dev / Google). Clarity lists the same “good” targets: LCP within 2.5 s, INP ≤ 200 ms, CLS ≤ 0.1. Clarity moved from FID to INP in January 2025.

LCP: Good ≤ 2.5 s (2500 ms); Needs improvement ≤ 4.0 s; Poor above that.
INP: Good ≤ 200 ms; Needs improvement ≤ 500 ms; Poor above that.
CLS: Good ≤ 0.1; Needs improvement ≤ 0.25; Poor above that.
This is not a live Lighthouse or Clarity project scan—paste values you already measured.
Website analysis only; not for native mobile app monitoring (Clarity note).

Example

Sample: LCP 3.2 s, INP 280 ms, CLS 0.18 → each metric Needs improvement, with image/JS/layout tips shown under each card.

Good fits

After reading Clarity Performance Overview or URL Performance, paste p75 LCP/INP/CLS to interpret grades offline.
Before and after image compression: compare LCP numbers from PSI or field data.
Teach the FID→INP change and the three page-experience metrics on one page.

Frequently asked questions

Where do the thresholds come from?

Good targets match Clarity Performance metrics and industry Core Web Vitals. Needs improvement / Poor bands follow the public web.dev / Google ranges listed under Rules.

Does this replace PageSpeed Insights or Clarity?

No. Use PSI, CrUX, or Clarity to measure; use this page to grade pasted numbers and read causes/fixes without uploading a URL here.

What about FID?

Clarity transitioned from FID to INP in January 2025. This tool grades INP only.

Are my numbers uploaded?

No. Values stay on your device in the browser tab and are not uploaded to a server.

Why mention the 75th percentile?

Clarity documents that LCP, INP, and CLS in the widget are the 75th percentile. Grade the same percentile you care about in your report.

Questions or feedback

Something unclear, broken, or missing? Draft a message below — we read every note about these tools.