Does PERF_RENDER_BLOCKING_SCRIPTS affect my score?

Yes. It is an importance 6 rule at SPECIFICATION confidence, so a failure costs 6 × 1 points of impact in the Performance category before that category is normalised to 100.

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_RENDER_BLOCKING_SCRIPTS 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 Affects your score

No render-blocking scripts in <head>

PERF_RENDER_BLOCKING_SCRIPTS

A synchronous script in the head halts HTML parsing until it downloads and executes, delaying first paint by exactly that long.

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How this rule is weighted

Importance: 6 / 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: warning; How the finding is presented when it fails.
Scoring: Counts; A failure costs points in its category.

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_RENDER_BLOCKING_SCRIPTS affect my score?: Yes. It is an importance 6 rule at SPECIFICATION confidence, so a failure costs 6 × 1 points of impact in the Performance category before that category is normalised to 100.
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_RENDER_BLOCKING_SCRIPTS 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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