A deep dive into LCP, CLS, and INP optimizations. How to eliminate layout shifts, optimize font loading, and minimize client-side bundle weight.
# Achieving 100/100 Core Web Vitals in Next.js 15
Web performance directly correlates with user conversion rates and search engine rankings. In this technical walkthrough, we break down exact techniques to achieve a perfect 100 score across all Lighthouse metrics.
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## 1. Cumulative Layout Shift (CLS) Elimination
Layout shifts ruin user experience. To guarantee **CLS = 0**:
- Always define explicit width/height ratios or aspect-ratio CSS utilities for image containers.
- Reserve static font fallback height using `next/font` CSS variable loading.
- Avoid dynamically prepending un-sized elements above the fold.
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## 2. Largest Contentful Paint (LCP) Acceleration
- **Preconnect Critical Origins**: Add `preconnect` tags for font & analytics domains.
- **Image Priority**: Use `priority` props on hero images so they load before deferred JavaScript scripts.
- **AVIF / WebP Formats**: Configure Next.js `images.formats: ['image/avif', 'image/webp']` for 40% compression improvements.
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## Summary
Performance is an ongoing engineering discipline, not a one-off task. By enforcing automated Lighthouse audits in CI/CD, we maintain sub-second speed consistently.