Search engines crawl your HTML and may run JavaScript to see content. What they get from the initial response and how fast the page loads both influence ranking. As a frontend developer you own structure, metadata, and performance.

Semantic HTML and a clear hierarchy help crawlers understand the page. Slow or heavy pages and content that only appears after JS runs can hurt SEO unless you use SSR/SSG or pre-render.

Each page should have a unique title and meta description; they appear in search results and affect click-through. Use h1–h6 in a logical order (one h1 per page). Add alt text to images so crawlers and screen readers know what they show.

For SPAs, critical content should be in the initial HTML or delivered via server-side or static rendering. If the crawler only sees a shell and content loads later, it may not index that content well.

LCP (Largest Contentful Paint), FID (First Input Delay), and CLS (Cumulative Layout Shift) are ranking factors. Optimize images (format, size, lazy-load), reduce and split JS, and reserve space for dynamic content to avoid layout shift.

Measure with Lighthouse or PageSpeed Insights; fix the biggest wins first. [MDN – Web performance](https://developer.mozilla.org/en-US/docs/Learn_web_development/Getting_started).