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Performance Lab · LAB-05Under investigation

“100 Lighthouse means your website is perfect.”

Lighthouse is a synthetic run on a simulated device, on your network, with no real user in sight. It is a useful ratchet, not a verdict.

Verdict
BUSTED
Level
DEVELOPER
Division
LAB-05
References
02

Investigation

Lighthouse measures a single cold load under simulated throttling. Real users arrive with warm caches and cold ones, on flaky networks, on devices five years older than yours, from further away, with extensions installed, and they interact, which is where INP lives and where synthetic runs have the least to say.

Lab (Lighthouse)Field (CrUX / RUM)
Question answeredDid my change help?What did users experience?
VarianceLow, reproducibleHigh, real
Interaction coverageMinimalComplete
Device profileOne simulated deviceEverything your users own

References

  1. 01ChromeLighthouse documentation
  2. 02web.devLab and field data