Total Blocking Time [TBT]

Total Blocking Time
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Total Blocking Time (TBT) is used as part of Core Web Vitals to measure in milliseconds (ms) how responsive your website is to user input. Essentially, TBT measures the amount of time your web page was blocked, preventing the user from interacting with it.

If the main thread of your page load is blocked, your page can’t respond to user actions like screen taps, keyboard actions, or mouse clicks. Therefore, optimising your TBT can often make one of the most impactful improvements in your website’s responsiveness.

The TBT is believed to account for 25% of your PageSpeed Insights score, so getting this right is key to a good score.

You can use Chrome DevTools to see all the main thread processes in the performance tab and identify which are taking the most time to load.

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