Is Time To Interactive calculated by WPT?

WebPageTest General Discussion
1

I know Time To Interactive is becoming an important metric, but having a hard time figuring out if this is calculated by WebPageTest or not?

I see the documentation here, but that seems more of a lesson than an explanation for WPT

This thread implies it is being calculated (assuming domInteractive?), yet this thread gives me the impression it’s something we need to calculate on our own?

Is it domInteractive or something that’s not built in??

Thanks in advance,
Shane

2

Hi
That’s built-in but relatively hidden
First you have to be on Chrome, then you have to run a test that captures the Chrome Devtools timeline, and at last you have access to the metric in the raw results, see here : https://www.webpagetest.org/xmlResult.php?testId=180927_JD_7b16ccb6c695ea26e2d0b0067012a1c9

and look for TTIMeasurementEnd, LastInteractive or interactivePeriods.

Depending on a factor I did not understood, the TimeToInteractive sometimes is calculated by Webpagetest, and sometimes not.
When it’s not the case, calculate it from the interactivePeriods keys

Hope this helps !

3

The metric is calculated in WPT but is only available in the Chrome browser.

Here is a great article on this which provides more detail - Web Performance Calendar » Time To Interactive – Measuring more of the user experience

FYI rather than just use the TTI alone, I prefer to also look at the horizontal bar Page is Interactive to see the points at which the page is interactive or not. This can provide valuable insight as to the periods of time it is interactive or not.

The thread you reference was intended to clarify the misconceptions on the use of DomInteractive as a way to measure when the page is actually interactive.

4

Thank you so much - enabling Chrome Dev Tools Timeline was the key that I needed.

Okay now I see the extra data, but still a little confused on which one is ‘TTI’? The UI reports a value for ‘First Interactive (beta)’, yet in the raw response that value used is ‘LastInteractive’. Why would the UI be labeling Last Interactive as First Interactive?

The documentation discusses “Time to Consistently Interactive” vs “Time to First Interactive”, but doesn’t specify which of those is indicated in the raw data.

Thank you again

5

Update - I ran some more tests, and noticed FirstInteractive, LastInteractive, and TimeToInteractive in the raw data. Looked at the code in github and the value of the ‘First Interactive (beta)’ is mapped to the ‘FirstInteractive’ value.

So I’m going to consider FirstInteractive as the TTI metric…someone correct me if I’m wrong :slight_smile: