TL;DR
A long task is any task that occupies the browser main thread for more than 50 milliseconds, blocking it from responding to user input or rendering updates during that period.
What is Long Tasks?
A long task is any task that occupies the browser main thread for more than 50 milliseconds, blocking it from responding to user input or rendering updates during that period.
Learn more in our how to improve long tasks guide, or work with us through our done-for-you speed optimization service.
How Long Tasks is Measured
Long tasks are reported by the Long Tasks API and visible in the Performance panel of Chrome DevTools and in Lighthouse.