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 is a suite of tools for running Google Lighthouse audits in CI pipelines. The most common GitHub Actions integration uses 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,
  "currentScore": 87,
  "delta": -8,
  "status": "regressed",
  "newFailures": ["color-contrast", "image-alt"],
  "newPasses": []
}

Regression Thresholds

Each delta, with its severity and action.

Delta	Severity	Action
Score drops 10+ points	Critical	Immediate attention, likely multiple new violations
Score drops 5-9 points	Serious	New violations introduced, review before merge
Score drops 1-4 points	Moderate	Minor regression, track for follow-up
Score unchanged or improved	N/A	No regression detected

Structured Output Format

When lighthouse-bridge normalizes Lighthouse data, it produces findings in this format:

{
  "source": "lighthouse-ci",
  "ruleId": "color-contrast",
  "wcagCriterion": "1.4.3",
  "wcagLevel": "AA",
  "severity": "serious",
  "confidence": "high",
  "url": "https://example.com/login",
  "element": "button.submit-btn",
  "description": "Element has insufficient color contrast ratio",
  "lighthouseWeight": 7,
  "lighthouseScore": {
    "overall": 87,
    "previousOverall": 95,
    "delta": -8,
    "status": "regressed"
  }
}

GitHub Actions Integration

treosh/lighthouse-ci-action

The most common Lighthouse CI GitHub Action:

- name: Run Lighthouse CI
  uses: treosh/lighthouse-ci-action@v12
  with:
    urls: |
      https://example.com
      https://example.com/about
    uploadArtifacts: true
    configPath: ./lighthouserc.json

Action Inputs

Each input, with its required and description.

Input	Required	Description
urls	Yes (or in config)	Newline-separated URLs to audit
configPath	No	Path to Lighthouse CI config file
uploadArtifacts	No	Upload HTML reports as workflow artifacts
temporaryPublicStorage	No	Upload to temporary public storage for sharing
runs	No	Number of runs per URL (default: 1)
budgetPath	No	Path to a Lighthouse budget JSON file

Extracting Results from Artifacts

Lighthouse CI uploads results as workflow artifacts. To retrieve scores:

1. Download the artifact from the workflow run
2. Parse the JSON report files
3. Extract categories.accessibility.score for the overall score
4. Extract individual audits.{audit-id} results for violations