Why is FCP greater than LCP ?

[pschonmann]

Your question

FCP is greater than LCP, that doesnt make sense

root@docker1:~# docker run --rm -v "$(pwd)":/sitespeed.io sitespeedio/sitespeed.io:latest https://www.argul.cz -b chrome
Google Chrome 130.0.6723.58 
Mozilla Firefox 131.0
Microsoft Edge 129.0.2792.89 
[2024-11-07 02:04:29] INFO: Versions OS: linux 5.10.0-28-amd64 nodejs: v20.17.0 sitespeed.io: 35.3.1 browsertime: 23.2.0 coach: 8.0.2
[2024-11-07 02:04:29] INFO: Running tests using Chrome - 3 iteration(s)
[2024-11-07 02:04:30] INFO: Testing url https://www.argul.cz iteration 1
[2024-11-07 02:04:40] INFO: Take after page complete check screenshot
[2024-11-07 02:04:41] INFO: Take cumulative layout shift screenshot
[2024-11-07 02:04:42] INFO: Take largest contentful paint screenshot
[2024-11-07 02:04:45] INFO: Use the visual metrics portable script
[2024-11-07 02:04:45] INFO: Get visual metrics from the video
[2024-11-07 02:04:49] INFO: https://www.argul.cz TTFB: 117ms DOMContentLoaded: 674ms firstPaint: 494ms FCP: 494ms LCP: 420ms Load: 1.05s CLS:0.0021
[2024-11-07 02:04:49] INFO: VisualMetrics: FirstVisualChange: 500ms SpeedIndex: 1.35s VisualComplete85: 700ms LastVisualChange: 6.63s
[2024-11-07 02:04:49] INFO: Testing url https://www.argul.cz iteration 2
[2024-11-07 02:05:00] INFO: Take after page complete check screenshot
[2024-11-07 02:05:00] INFO: Take cumulative layout shift screenshot
[2024-11-07 02:05:01] INFO: Take largest contentful paint screenshot
[2024-11-07 02:05:04] INFO: Use the visual metrics portable script
[2024-11-07 02:05:04] INFO: Get visual metrics from the video
[2024-11-07 02:05:08] INFO: https://www.argul.cz TTFB: 110ms DOMContentLoaded: 625ms firstPaint: 496ms FCP: 496ms LCP: 407ms Load: 823ms CLS:0.0021
[2024-11-07 02:05:08] INFO: VisualMetrics: FirstVisualChange: 500ms SpeedIndex: 1.32s VisualComplete85: 666ms LastVisualChange: 6.43s
[2024-11-07 02:05:09] INFO: Testing url https://www.argul.cz iteration 3
[2024-11-07 02:05:19] INFO: Take after page complete check screenshot
[2024-11-07 02:05:20] INFO: Take cumulative layout shift screenshot
[2024-11-07 02:05:20] INFO: Take largest contentful paint screenshot
[2024-11-07 02:05:23] INFO: Use the visual metrics portable script
[2024-11-07 02:05:23] INFO: Get visual metrics from the video
[2024-11-07 02:05:27] INFO: https://www.argul.cz TTFB: 133ms DOMContentLoaded: 632ms firstPaint: 496ms FCP: 496ms LCP: 415ms Load: 825ms CLS:0.0021
[2024-11-07 02:05:27] INFO: VisualMetrics: FirstVisualChange: 500ms SpeedIndex: 1.33s VisualComplete85: 700ms LastVisualChange: 6.43s
[2024-11-07 02:05:27] INFO: https://www.argul.cz 76 requests, TTFB: 117ms (σ10.00ms 8.0%), firstPaint: 496ms (σ1.00ms 0.2%), firstVisualChange: 500ms (σ0.00ms 0%), FCP: 496ms (σ1.00ms 0.2%), DOMContentLoaded: 632ms (σ22.00ms 3.4%), LCP: 415ms (σ5.00ms 1.3%), CLS: 0.0021 (σ0.00 0%), TBT: 0ms (σ0.00ms 0%), CPUBenchmark: 43ms (σ3.00ms 7.7%), Load: 825ms (σ107.00ms 11.9%), speedIndex: 1.33s (σ13.00ms 1.0%), visualComplete85: 700ms (σ16.00ms 2.3%), lastVisualChange: 6.43s (σ94.00ms 1.5%) (3 runs)
[2024-11-07 02:05:28] INFO: The server responded with a 404 status code for https://www.argul.cz/favicon-16x16.png
[2024-11-07 02:05:28] INFO: The server responded with a 404 status code for https://www.argul.cz/favicon-16x16.png
[2024-11-07 02:05:28] INFO: The server responded with a 404 status code for https://www.argul.cz/favicon-16x16.png

[soulgalore]

Hi @pschonmann check if the LCP element is the correct element. If so, you can report Chrome bugs direct in https://issues.chromium.org/issues . If it seems to be the wrong element for LCP, let me know.

[pschonmann]

Im not sure if its only chromium thing. Im getting these weird results in Firefox and Edge -b option too. Anyway LCP seems to be identified okay. In chromium ctrl+shift+i and performace tab - LCP > img - same match as LCP on html report in first run.

root@docker1:~# docker run --rm -v "$(pwd)":/sitespeed.io sitespeedio/sitespeed.io:latest https://www.argul.cz -b firefox -n 1
Google Chrome 130.0.6723.58 
Mozilla Firefox 131.0
Microsoft Edge 129.0.2792.89 
[2024-11-07 06:34:59] INFO: Versions OS: linux 5.10.0-28-amd64 nodejs: v20.17.0 sitespeed.io: 35.3.1 browsertime: 23.2.0 coach: 8.0.2
[2024-11-07 06:34:59] INFO: Running tests using Firefox - 1 iteration(s)
[2024-11-07 06:35:01] INFO: Testing url https://www.argul.cz iteration 1
[2024-11-07 06:35:11] INFO: Take after page complete check screenshot
[2024-11-07 06:35:12] INFO: Take largest contentful paint screenshot
[2024-11-07 06:35:16] INFO: Use the visual metrics portable script
[2024-11-07 06:35:16] INFO: Get visual metrics from the video
[2024-11-07 06:35:20] INFO: https://www.argul.cz 86 requests, TTFB: 257ms, firstPaint: 825ms, firstVisualChange: 867ms, FCP: 813ms, DOMContentLoaded: 784ms, LCP: 684ms, CPUBenchmark: 60ms, Load: 1.12s, speedIndex: 1.73s, visualComplete85: 1.63s, lastVisualChange: 6.70s
[2024-11-07 06:35:20] INFO: The server responded with a 404 status code for https://popup-server.azurewebsites.net/zbozi/company/review/...
[2024-11-07 06:35:22] INFO: HTML stored in /sitespeed.io/sitespeed-result/www.argul.cz/2024-11-07-06-34-59
root@docker1:~# docker run --rm -v "$(pwd)":/sitespeed.io sitespeedio/sitespeed.io:latest https://www.argul.cz -b edge -n 1
Google Chrome 130.0.6723.58 
Mozilla Firefox 131.0
Microsoft Edge 129.0.2792.89 
[2024-11-07 06:35:33] INFO: Versions OS: linux 5.10.0-28-amd64 nodejs: v20.17.0 sitespeed.io: 35.3.1 browsertime: 23.2.0 coach: 8.0.2
[2024-11-07 06:35:33] INFO: Running tests using Edge - 1 iteration(s)
[2024-11-07 06:35:33] INFO: Using Edge is experimental at the moment and use the same configuration as for Chrome
[2024-11-07 06:35:34] INFO: Testing url https://www.argul.cz iteration 1
[2024-11-07 06:35:45] INFO: Take after page complete check screenshot
[2024-11-07 06:35:45] INFO: Take cumulative layout shift screenshot
[2024-11-07 06:35:46] INFO: Take largest contentful paint screenshot
[2024-11-07 06:35:49] INFO: Use the visual metrics portable script
[2024-11-07 06:35:49] INFO: Get visual metrics from the video
[2024-11-07 06:35:53] INFO: https://www.argul.cz 76 requests, TTFB: 155ms, firstPaint: 540ms, firstVisualChange: 533ms, FCP: 540ms, DOMContentLoaded: 768ms, LCP: 427ms, CLS: 0.0021, TBT: 0ms, CPUBenchmark: 41ms, Load: 928ms, speedIndex: 1.39s, visualComplete85: 733ms, lastVisualChange: 6.57s
[2024-11-07 06:35:54] INFO: The server responded with a 404 status code for https://www.argul.cz/favicon-16x16.png
[2024-11-07 06:35:55] INFO: HTML stored in /sitespeed.io/sitespeed-result/www.argul.cz/2024-11-07-06-35-33

[soulgalore]

Edge and Chrome use same codebase. You can report bugs for Firefox in https://bugzilla.mozilla.org. So the FCP and LCP is picked up from the browsers API:s, checkout https://w3c.github.io/paint-timing/#first-contentful-paint and https://w3c.github.io/largest-contentful-paint/#sec-largest-contentful-paint-interface, the values are not touched in Browsertime/sitespeed.io, they are picked up directly from the browser.

[pschonmann]

https://issues.chromium.org/issues/377724738