What is the visual monitoring diff threshold?
The diff threshold sets how much pixel change must accumulate before Lemwatch alerts — default 2% is right for most product pages.
Quick answer#
The threshold is the % of pixels that must change (after ignore-zone masking) before an alert fires. Default is 2%, which catches copy edits and layout shifts while ignoring anti-alias jitter.
Recommended thresholds#
Where to find it in Lemwatch#
Site → Visual Monitoring → <page> → Sensitivity.
FAQ#
Why not just alert on any pixel change?#
Browsers subtly re-render fonts and anti-aliasing between runs. 0% would page you constantly.
Related#
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Related Articles
How do CSS selectors work in visual monitoring?
Restrict visual monitoring to a specific region using a CSS selector so Lemwatch only diffs the part of the page that matters, like pricing or hero.
How do I stop visual monitoring flagging ads or rotating banners?
Draw ignore-zone rectangles on the screenshot so Lemwatch masks noisy regions (ads, timestamps, carousels) before comparing pixels.
Reducing false visual alerts
Cut noisy visual alerts from ads, timestamps, and personalised content without missing real changes.
Rotating content noise (visual + text diff)
Lemwatch scrubs rotating banners, timestamps, and random ads so they do not fire visual alerts.