perf.fcp-slow

What to change

A finding of this rule on a page carries the exact edits for that page: the markup it quotes, and what to write instead.

When it runs

Runs with --lighthouse, on the command or the local server. Info is a best practice: worth doing, rarely urgent, and --no-info leaves it out. Each finding takes 1 point off the page's score.

The severity here is the rule's usual one: a finding can be raised or lowered when the page gives a reason.

Run it, or skip it

Check a page for this rule alone, after a fix for instance:

npx @rivi-software/agentic-seo-check audit https://example.com --lighthouse --rule perf.fcp-slow

Or from an assistant, with the MCP tool seo_audit_page:

{
  "url": "https://example.com",
  "lighthouse": true,
  "rules": [
    "perf.fcp-slow"
  ]
}

To leave it out of an audit, pass --disable perf.fcp-slow on the command, or disableRules: ["perf.fcp-slow"] to a tool.

• Infoperf.field-cls-needs-improvementOn phones, the layout of real visits shifts by more than 0.10 at the 75th percentile: Cumulative Layout Shift (CLS) in the Chrome UX Report's last 28 days, for the page's URL or, when it has too few visits, its origin. Google rates it as needing improvement.
• Warningperf.lcp-slowLargest Contentful Paint above 2.5 s (poor above 4 s). Lab measurement from Lighthouse.
• Warningperf.cls-highCumulative Layout Shift above 0.1 (poor above 0.25).
• Warningperf.tbt-highTotal Blocking Time above 200 ms (poor above 600 ms). Lab proxy for Interaction to Next Paint.
• Warningperf.ttfb-slowServer response time (TTFB) above 800 ms.
• Warningperf.score-lowLighthouse performance score below 50.
• Infoperf.opportunityA Lighthouse opportunity with measurable estimated savings.
• Warninglighthouse.seo-audit-failedA Lighthouse SEO audit failed (rendered-DOM checks such as crawlable anchors, robots.txt validity).