Why do some of my Chrome tabs have a blue dot on them like this?
This means that the title has changed. Chrome used to indicate this with a more subtle effect as described in this question: Pinned tab on Google Chrome has a rippling or highlighting effect
It can also mean that a dialog is open on that page, such as an alert or print dialog.
alert, URL Protocol launch permission prompt, print preview) showing on the background tab and it wants attention.  bugs.chromium.org/p/chromium/issues/detail?id=482776#c38– EricLawOct 13, 2022 at 16:09
It means that there is a change of status on that page. The page has changed.
It would also show up in case there is an alert popup.
To view this in action, open 2 tabs. In the first page open console and type:
and press enter.
Then navigate to 2nd tab. After
5 sec, you will see a blue dot on the first tab.
Can you provide a bit more detail as to what an
alertpop up is? Dec 21, 2018 at 16:12