Make NO_LCP error message specific to LCP

[vsteenhoudt]

FAQ

• Yes, my issue is not about variability or throttling.
• Yes, my issue is not about a specific accessibility audit (file with axe-core instead).

URL

https://jsbin.com/pajibab/edit?html,output

What happened?

When analyzing page load with mode: navigation, device: mobile and categories: performance there is an error on the LCP metric.
We receive the following message:
Something went wrong with recording the trace over your page load. Please run Lighthouse again. (NO_LCP)

This error error does not occur when analyzing page load desktop on desktop.

What did you expect?

Would have expected a similar result as when running the test on desktop. Where the error does not occur.

What have you tried?

Made a minimal html page with only the image with css style object-fit: cover defined to make sure nothing else might be causing the issue.

How were you running Lighthouse?

Chrome DevTools

Lighthouse Version

9.6.6

Chrome Version

107.0.5304.110

Node Version

No response

OS

Mac

Relevant log output

No response

[adamraine]

This is intentional and it's not connected to object-fit. Images that fill the entire viewport are not considered LCP candidates.

[romainmenke]

Something went wrong with recording the trace over your page load. Please run Lighthouse again. (NO_LCP)

Is the error message maybe to alarming for this case?

If the outcome (NO_LCP) is expected in this case then we can assume that nothing went wrong with the recording and that running Lighthouse again won't solve anything.

[adamraine]

Is the error message maybe to alarming for this case?

Yeah, a lot of the NO_LCP cases aren't actually fixed by running Lighthouse again. This message is used for several errors relating to the trace, but we could use something more specific to LCP.

I would support rephrasing this message to something like:

"The page did not paint anything that qualifies as LCP. Ensure the page has a valid LCP element and then try again. (NO_LCP)"

[romainmenke]

Thank you @adamraine for this speedy update!

The new message is much clearer imo.