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How to Fix HTML Errors in Static-Site Generators

Static-site generators (Astro, Hugo, Eleventy, Gatsby) produce raw HTML at build time. Validation should happen as part of the build pipeline. This guide covers SSG-specific HTML validation. Pair with HTML Checker guide.

Step-by-step: How to fix HTML errors in static-site generators

  1. Build the site. npm run build (Astro, Gatsby, Eleventy) or hugo (Hugo). Output goes to dist/, public/, or _site/ depending on framework.
  2. Run html-validate on built output. npm install --save-dev html-validate. Configure .htmlvalidate.json with desired rules. Run: npx html-validate 'dist/**/*.html'. Reports invalid HTML per file.
  3. Identify template-source errors. Most SSG HTML errors come from templates with bugs (Hugo .html templates, Astro .astro files, Eleventy .njk templates). Trace error from built file back to its template source.
  4. Fix Markdown-to-HTML quirks. Markdown content rendered to HTML sometimes produces unexpected structure: lists not wrapped in <ul>, paragraphs interrupted by HTML blocks, rough <br> handling. Configure your Markdown processor (marked, remark, goldmark) to handle edge cases.
  5. Fix layout/wrapper errors. Common: layouts wrap content in <p> tags, then content includes block elements (becomes <p><div>...</div></p> — invalid). Audit layout templates: use <div> not <p> for content wrappers.
  6. Add html-validate to CI. GitHub Actions or other CI: build site → run html-validate → fail build if errors. Catches regressions before deployment.
  7. Periodic W3C validation. Beyond CI: monthly W3C validator runs on production URLs. Catches edge cases CI missed.
Tip. Pin your framework, dependency, and config versions in a single internal doc (Next.js version, React version, rendering strategy choices, custom config). When something breaks after a framework or library update, you have a baseline to compare against.

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Frequently Asked Questions

Which SSG produces cleanest HTML out of the box?

Astro and Eleventy typically produce cleanest HTML — they're HTML-first frameworks with explicit templates. Hugo also produces clean HTML. Gatsby (React-based) has more HTML quirks due to JSX-to-HTML compilation, similar to Next.js patterns. Astro and Eleventy lead for HTML hygiene.

How does Astro compare to React for HTML validity?

Astro defaults to zero JavaScript on the client and uses HTML/CSS/component syntax. Output HTML is direct and typically cleaner than React JSX output. Astro components ('.astro' files) compile to static HTML by default with optional islands of interactivity. Strong for HTML hygiene.

Can I run html-validate on Hugo output?

Yes. Build Hugo (hugo command), then npx html-validate 'public/**/*.html'. Configure rules in .htmlvalidate.json. Hugo's template language (Go templates) generally produces valid HTML; errors usually come from custom template logic.

Why do Markdown blog posts produce HTML validation errors?

Markdown processors (marked, remark, goldmark) handle edge cases differently. Common: HTML blocks inside paragraphs break <p>; nested lists may not nest correctly; raw HTML in Markdown may bypass safety checks. Solution: use a strict Markdown processor configuration and validate output.

Should I configure html-validate strictness for SSGs?

Yes — start strict, ease selectively. Recommended initial config: extend html-validate:recommended preset. Disable rules that fight your framework patterns (some SSGs intentionally use HTML5 features W3C strict mode flags). Goal: zero true errors; ignore framework-specific noise.

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