The Scripts You Didn't Write Are Slowing Down Your App

I once audited a page where nearly 40% of the main thread blocking time came from a tag manager firing scripts that the engineering team didn't know were still active. Analytics from a vendor they'd switched away from. A heatmap tool from a trial nobody cancelled. A pixel for an ad campaign that ended months ago. Nobody wrote those scripts. They accumulated. What third-party scripts actually cost you The performance impact happens in two places: network and main thread. On the network side, each