Does HTML_DUPLICATE_IDS affect my score?

Yes. It is an importance 7 rule at SPECIFICATION confidence, so a failure costs 7 × 1 points of impact in the HTML 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 HTML_DUPLICATE_IDS 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 HTML checker and in a full scan.

HTMLHigh Affects your score

Element ids stay unique

HTML_DUPLICATE_IDS

Duplicate ids break getElementById, label/for association, aria-labelledby and in-page anchors - all of which silently resolve to the first match only.

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How this rule is weighted

Importance: 7 / 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: error; 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 HTML_DUPLICATE_IDS affect my score?: Yes. It is an importance 7 rule at SPECIFICATION confidence, so a failure costs 7 × 1 points of impact in the HTML 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 HTML_DUPLICATE_IDS 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 HTML checker and in a full scan.

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