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Front-End’s Missing Metric: The TBT Window
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The TBT Window is the FCP-to-TTI interval used to calculate Total Blocking Time. If FCP or TTI moves, TBT can change even when long tasks do not.
Source:https://csswizardry.com/2026/06/front-ends-missing-metric-the-tbt-window/PreviousWeb-Perf Wednesday 001 – SPAs Are Finally Becoming MeasurableNextMeet Your Users Where They Are with Obs.js