Does PERF_VARY affect my score?

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

What does SPECIFICATION confidence mean?

A standard says so: HTML, WCAG, an RFC or Google's own documentation. 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_VARY 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.

PerformanceLow Detection only

Vary header present

PERF_VARY

Vary tells caches which request headers change the response, preventing wrong cached variants being served.

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How this rule is weighted

Importance: 2 / 10; How much this matters relative to other rules.
Confidence: SPECIFICATION; A standard says so: HTML, WCAG, an RFC or Google's own documentation.
Severity: info; 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_VARY affect my score?: No. It is a detection rule: it runs, appears in your report and never penalises you. "Vary header present" is information about the page rather than a defect - most pages are not expected to satisfy it.
What does SPECIFICATION confidence mean?: A standard says so: HTML, WCAG, an RFC or Google's own documentation. 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_VARY 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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