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Flash of original content (FOOC)

FOOC is when visitors briefly see the original page before a client-side test applies the variant.

Written by Reflective Data experts · updated Oct 5, 2026

It happens when the testing script loads after the page starts rendering. The flicker can affect user experience and bias results, because users notice something change.

Fixes include loading the script early, using anti-flicker snippets sparingly, or moving to server-side testing.

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A/B testClient-side testingServer-side testing

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