On-Page SEO Score: How a Single 0-100 Number Is Calculated

## Why it matters

The number isn't a Google metric; it's a prioritisation tool. Its real value is in the weighting: a broken indexability check should tank the score far more than a slightly long meta description, so an honest score reflects actual ranking risk rather than just counting how many boxes are checked.

A 100-point checklist where every item counts equally toward one score is useless. Fixing a missing canonical URL moves the needle far more than optimising keyword density. A well-weighted score forces you to focus on the high-impact issues first.

## How it works

An on-page SEO score aggregates multiple checks (typically 10 to 20) across metadata, structure, and content. Each check is assigned a weight reflecting its actual impact on search visibility. Indexability and canonical issues carry high weight because they can silently remove a page from Google's index. Title and meta description carry moderate weight because they affect ranking likelihood and click-through rate. Cosmetic issues carry low weight.

The raw scores from each check (0-100 for each) are multiplied by their assigned weights, summed, and normalised back to 0-100 for the overall score. This produces a number that actually reflects the priority of fixes.

## What does not matter

Achieving a perfect 100 score does not guarantee a page will rank. No auditor score correlates strongly with rankings because ranking depends on topical authority, backlinks, user signals, and content quality (none of which a local on-page tool can fully measure).

A 95 score is not meaningfully better than an 85. The score is ordinal (good relative to broken) not cardinal (predictive of rank position). It is a starting point for diagnostics, not an end goal. Many high-ranking pages have lower scores because they excel at aspects the tool cannot measure.

## Code example

A weighted scoring rubric example (not the full formula, illustrative):

Check                    | Weight | Score | Weighted
Indexability              | 30%    | 90    | 27
Canonical Tag             | 20%    | 100   | 20
Title Tag                 | 15%    | 70    | 10.5
Meta Description          | 15%    | 80    | 12
Heading Structure (H1-H6) | 10%    | 60    | 6
Images with Alt Text      | 5%     | 100   | 5
Structured Data           | 5%     | 0     | 0
------
Total Score (weighted)                    | 80.5 (rounded to 81)
Letter Grade                              | B
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A page with critical indexability issues:

<!-- This page has a broken canonical - high-weight fail -->
<link rel="canonical" href="https://example.com/old-page">
<!-- But this page is actually https://example.com/new-page -->
<!-- Result: indexability check fails, score drops to ~40-50 -->
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## How Scalpel shows it

Scalpel SEO's Overview panel displays the composite score and letter grade prominently, with a detailed breakdown below showing the individual check results and their weights. This breakdown lets you see at a glance which issues to fix first - the high-weight items that actually matter for search visibility.