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    Visual monitoring

    How do I detect visual changes on a website?

    Part of Visual monitoring — the full answer, the facts and the alternatives in one place.

    Quick answer

    How do I detect visual changes on a website?

    Point a visual-monitoring tool at the URL, set an hourly or daily check, and it screenshots the page, diffs each capture against the last baseline, and alerts when the visual difference crosses a 2–5% threshold.

    • Pixel-diffs need noise scrubbing — timestamps, session IDs and animated banners must be masked.
    • CSS selector ignore-zones prevent false positives on carousels, chat widgets and cookie banners.
    • Text-diff on the rendered DOM catches content edits that pixel-diffs miss (e.g. price changes).
    • Full-page vs viewport captures matter: viewport for above-the-fold, full-page for compliance.

    Step-by-step

    1. 1
      Add the URL

      Add the exact URL you want watched — one entry per unique visual state.

    2. 2
      Mask dynamic zones

      Use CSS selectors to exclude carousels, chat widgets and cookie banners from the diff.

    3. 3
      Pick an interval

      Hourly for pricing / checkout; daily for marketing pages and blog posts.

    4. 4
      Set the threshold

      Start at 3%. Tune down if you get false positives, up if real changes are missed.

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    Last verified: by the Lemwatch research team.

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