Time to Interactive (TTI)

First Interactive and Consistently Interactive help pinpoint the time at which a given page is ready for human interaction.

Why is monitoring Time to Interactive important?

Time to Interactive is influenced by how long it takes for a page to be fully rendered and the amount of JavaScript Main Thread activity. Pages that have a large amount of scripting will delay the time to interaction.

JavaScript execution greatly affects user experience, yet is often ignored by developers. Scripting performance varies greatly from device to device—slower CPUs spend far more time parsing and compiling, than faster ones.

How are these metrics calculated?

Calibre observes the points at which a given page has:

  • Finished rendering content
  • Key webfonts are visible and the interface has stopped moving
  • The main JavaScript thread has no major activity

Major activity is categorised as JavaScript tasks that take longer than 50ms.

Calibre works backwards from the time of document completion until it finds a point at which the browser is at rest, users are able to fully read content and interact without notable delay.

Calibre tracks the following Time to Interactive metrics: First Interactive and Consistently Interactive. These are great candidates for improving the user experience.