How to Check HTML Validity in GitHub Actions

html-validate parses your markup and reports invalid nesting, unclosed elements, and disallowed attributes.

Point html-validate at your built HTML files. It exits non-zero on any error so malformed markup fails CI.

Steps

• Install html-validate and add an .htmlvalidate.json config.
• Build the site so the HTML output exists.
• Run html-validate over the output glob.

Config

// .htmlvalidate.json
{
  "extends": ["html-validate:recommended"]
}

Workflow

jobs:
  html-validity:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
      - run: npm ci && npm run build
      - run: npx html-validate 'dist/**/*.html'

Gotchas

• For framework templates, validate the rendered HTML output, not the raw template files.
• The Nu Html Checker (vnu) is an alternative when you want the same engine the W3C validator uses.

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