/kb-lighthouse-scanner

name: kb-lighthouse-scanner
description: Reference data, not a reviewer. Integrate Lighthouse CI accessibility audits. Detects configuration, parses results, maps findings to severity model, and tracks score regressions.
license: MIT
disable-model-invocation: true
user-invocable: false
metadata:
  tier: reference
  domain: cross-cutting
  output: none
  effort: low
  title: Lighthouse Scanner

Lighthouse CI Accessibility Integration

What Is Lighthouse CI?

[Lighthouse CI](https://github.com/GoogleChrome/lighthouse-ci) is a suite of tools for running Google Lighthouse audits in CI pipelines. The most common GitHub Actions integration uses [`treosh/lighthouse-ci-action`](https://github.com/treosh/lighthouse-ci-action).

Lighthouse provides:

• Performance, accessibility, best practices, and SEO scoring (0-100)
• Individual audit results with pass/fail status and detailed findings
• Score budgets and assertions to fail builds on regressions
• HTML and JSON report artifacts
• Score comparison across runs for trend tracking

**Accessibility focus:** The Lighthouse accessibility category runs a subset of axe-core rules and reports a weighted score from 0-100 along with individual audit violations.

Detecting Lighthouse CI Presence

Workflow File Detection

Search for workflow files referencing Lighthouse CI:

# Search for the treosh Lighthouse CI action
grep -rl "treosh/lighthouse-ci-action" .github/workflows/

# Search for official Lighthouse CI CLI usage
grep -rl "lhci autorun\|lighthouse-ci" .github/workflows/

**Patterns to match in YAML:**

- uses: treosh/lighthouse-ci-action@v12

Configuration File Detection

Lighthouse CI uses configuration files in the repository root:

# Check for Lighthouse CI config files
ls lighthouserc.js lighthouserc.json .lighthouserc.js .lighthouserc.json .lighthouserc.yml 2>/dev/null

| Config File | Format | |------------|--------| | `lighthouserc.js` | JavaScript module | | `lighthouserc.json` | JSON | | `.lighthouserc.js` | JavaScript module (dotfile) | | `.lighthouserc.json` | JSON (dotfile) | | `.lighthouserc.yml` | YAML (dotfile) |

Configuration Structure

Key fields in Lighthouse CI config:

{
  "ci": {
    "collect": {
      "url": ["https://example.com", "https://example.com/about"],
      "numberOfRuns": 3
    },
    "assert": {
      "assertions": {
        "categories:accessibility": ["error", {"minScore": 0.9}]
      }
    },
    "upload": {
      "target": "temporary-public-storage"
    }
  }
}

| Section | Purpose | Agent Use | |---------|---------|-----------| | `ci.collect.url` | URLs to audit | Scope of CI scanning | | `ci.collect.numberOfRuns` | How many times to run each URL | Reliability indicator | | `ci.assert.assertions` | Score budgets and thresholds | Regression detection | | `ci.upload.target` | Where to store reports | Report retrieval |

Parsing Lighthouse Accessibility Results

Accessibility Score

Lighthouse computes a weighted accessibility score from 0-100 based on individual audit results.

| Score Range | Grade | Interpretation | |-------------|-------|---------------| | 90-100 | A | Good accessibility | | 70-89 | B-C | Some issues to address | | 50-69 | D | Significant issues | | 0-49 | F | Critical accessibility failures |

Individual Audit Results

Each Lighthouse accessibility audit corresponds to an axe-core rule:

| Audit ID | axe-core Rule | WCAG Criterion | Weight | |----------|--------------|----------------|--------| | `image-alt` | `image-alt` | 1.1.1 | 10 | | `color-contrast` | `color-contrast` | 1.4.3 | 7 | | `label` | `label` | 1.3.1 | 7 | | `button-name` | `button-name` | 4.1.2 | 7 | | `link-name` | `link-name` | 2.4.4 | 7 | | `html-has-lang` | `html-has-lang` | 3.1.1 | 7 | | `document-title` | `document-title` | 2.4.2 | 7 | | `heading-order` | `heading-order` | 1.3.1 | 3 | | `meta-viewport` | `meta-viewport` | 1.4.4 | 10 | | `bypass` | `bypass` | 2.4.1 | 7 | | `tabindex` | `tabindex` | 2.4.3 | 7 | | `aria-allowed-attr` | `aria-allowed-attr` | 4.1.2 | 10 | | `aria-hidden-body` | `aria-hidden-body` | 4.1.2 | 10 | | `aria-required-attr` | `aria-required-attr` | 4.1.2 | 10 | | `aria-roles` | `aria-roles` | 4.1.2 | 7 | | `aria-valid-attr-value` | `aria-valid-attr-value` | 4.1.2 | 7 | | `aria-valid-attr` | `aria-valid-attr` | 4.1.2 | 10 |

Severity Mapping

Lighthouse uses weights rather than impact levels. Map to the agent severity model based on weight and audit pass/fail:

| Lighthouse Weight | Audit Status | Agent Severity | |------------------|-------------|---------------| | 10 | Fail | Critical | | 7 | Fail | Serious | | 3 | Fail | Moderate | | 1 | Fail | Minor | | Any | Pass | N/A (not reported) |

Correlation with Local Scans

Lighthouse-to-axe-core Mapping

Since Lighthouse uses axe-core under the hood, correlation is straightforward:

1. **Match by audit/rule ID:** Lighthouse audit IDs correspond directly to axe-core rule IDs 2. **Match by URL:** Compare scanned URLs from Lighthouse config with local scan targets 3. **Boost confidence:** Findings confirmed by both Lighthouse CI and local axe-core scan receive `high` confidence

Source Comparison

Each scenario, with its interpretation and action.

| Scenario | Interpretation | Action | |----------|---------------|--------| | Found by Lighthouse AND local scan | High confidence | Report as high confidence, full severity weight | | Found by Lighthouse only | Environment-specific | Report as medium confidence, note "CI-only finding" | | Found by local scan only | Not covered by Lighthouse subset | Report as medium confidence, note "local-only finding" | | Lighthouse score regressed | New accessibility issues introduced | Flag as regression, prioritize in report |

Score Regression Detection

Track Lighthouse accessibility scores across runs to detect regressions:

Comparing Scores

{
  "url": "https://example.com",
  "previousScore": 95,