Lighthouse.

Lighthouse is the audit tool built into Chrome DevTools (and at pagespeed.web.dev). It runs your site against a checklist and returns four 0–100 scores: Performance, Accessibility, Best Practices, and SEO.

Score targets for a healthy small-business site: 80+ on mobile Performance, 95+ on Accessibility and Best Practices, 100 on SEO. The SEO score is the easiest to ace — it's mostly checking that you have title tags, meta descriptions, valid schema, and a robots.txt.

Lighthouse uses a simulated slow connection, so the numbers are usually worse than what real visitors experience. Don't obsess over the exact score — fix the actionable items it flags.