Does PERF_IMAGE_SIZES_ATTR affect my score?

No. It is a detection rule: it runs, appears in your report and never penalises you. "Image sizes attribute present" is information about the page rather than a defect - most pages are not expected to satisfy it.

What does RESEARCH confidence mean?

Backed by large-sample study or industry research, not a specification. Confidence is a declared tier rather than a per-rule number, so every rule backed by the same class of evidence carries the same weight - which is what makes the score reproducible instead of hand-tuned.

How do I check PERF_IMAGE_SIZES_ATTR on my own site?

Paste your URL into the box above and it runs only this rule, usually in a couple of seconds. It is also included in the Performance checker and in a full scan.

PerformanceMedium Detection only

Image sizes attribute present

PERF_IMAGE_SIZES_ATTR

sizes tells the browser how large the image renders so it can pick the right srcset candidate.

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How this rule is weighted

Importance: 2 / 10; How much this matters relative to other rules.
Confidence: RESEARCH; Backed by large-sample study or industry research, not a specification.
Severity: warning; How the finding is presented when it fails.
Scoring: Excluded; Reported in the report, never penalised.

Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.

Questions about this rule

Does PERF_IMAGE_SIZES_ATTR affect my score?: No. It is a detection rule: it runs, appears in your report and never penalises you. "Image sizes attribute present" is information about the page rather than a defect - most pages are not expected to satisfy it.
What does RESEARCH confidence mean?: Backed by large-sample study or industry research, not a specification. Confidence is a declared tier rather than a per-rule number, so every rule backed by the same class of evidence carries the same weight - which is what makes the score reproducible instead of hand-tuned.
How do I check PERF_IMAGE_SIZES_ATTR on my own site?: Paste your URL into the box above and it runs only this rule, usually in a couple of seconds. It is also included in the Performance checker and in a full scan.

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