A/B Testing Tools Cost 10.2 Points of Good LCP, the Worst of Any Third-Party Category

    Sites running an A/B testing tool are good on LCP just 58.5% of the time on mobile versus 68.7% without, a 10-point loading penalty and the steepest of any third-party category we measured.

    Good loading (LCP) by third-party category, mobile penalty
    A/B testing tools
    10.2 pts
    Live chat widgets
    9.5 pts
    Google Tag Manager
    5.3 pts
    Cookie banners
    3.7 pts

    Source: PageSpeed Matters analysis of 9.5 million origins with CrUX field data, mobile 75th percentile, mid-2026. Bars scaled to the largest penalty.

    A/B testing sits at the top of the list. The anti-flicker snippet is the reason its loading cost outruns every other named tool.

    Core Web Vitals pass rate, with and without an A/B tool (mobile)
    Without an A/B tool
    42.4%
    With an A/B tool
    41.5%

    Source: PageSpeed Matters, mobile 75th-percentile field data, mid-2026.

    Overall pass barely moves because A/B tools live on stronger sites. The loading damage is real; the site quality masks it.

    Source: A/B Testing Tools Cost 10.2 Points of Good LCP, the Worst of Any Third-Party Category - PageSpeed Matters