Core Web Vitals in Next.js: Boost Performance, Credibility & SEO

In today’s digital landscape, user experience isn't just a nice-to-have—it's a growth engine. Google’s Core Web Vitals are a key factor in both SEO ranking and user retention. If you're building with Next.js, especially using the App Router, you're in a great position to optimize performance out of the box.

In this post, we'll cover:

- What are Core Web Vitals?

- How to measure them in Next.js

- How to optimize each (LCP, CLS, TTFB)

- Open source tools to help

Let's get started!

What Are Core Web Vitals?

Core Web Vitals are a set of three performance metrics defined by Google:

1. LCP (Largest Contentful Paint) – Measures loading speed. Should be < 2.5s.

2. CLS (Cumulative Layout Shift) – Measures visual stability. Should be < 0.1.

3. TTFB (Time to First Byte) – Measures server response time. Should be < 800ms.

These vitals are measurable, actionable, and directly impact SEO rankings.

⚙️ Measuring Core Web Vitals in Next.js

1. Using Next.js Built-in Analytics

With App Router, you can integrate next/script to load Google Analytics, or use Vercel’s built-in Analytics to track Web Vitals directly—ensuring your payload stays clean and compatible with rich text rendering.

1// app/web-vitals.ts
2export function reportWebVitals(metric) {
3  console.log(metric);
4  // send to analytics backend if needed
5}
6
7export const config = {
8  reportWebVitals: true,
9};

2. With Vercel Analytics

If you're deploying to Vercel, enable Web Analytics from your dashboard. It tracks Core Web Vitals in real-time.

Optimizing LCP in Next.js

LCP usually depends on:

- Hero image

- Large headlines

- Main content blocks

Tips:

- Use next/image for optimized image delivery.

- Preload critical images via <link rel="preload">

- Lazy load below-the-fold content

1<Image
2  src="/hero.jpg"
3  alt="Hero"
4  width={1200}
5  height={600}
6  priority
7/>

Optimizing CLS in Next.js

CLS is affected by:

- Fonts loading late

- Images without width/height

- Dynamic content injections

Tips:

- Set width/height on all media

- Reserve space for dynamic elements

- Use font-display: swap

1/* Reserve space for buttons, headers */
2.button {
3  min-height: 48px;
4}

Optimizing TTFB in Next.js

TTFB is mostly about backend speed. With App Router and Next.js 14+:

Tips:

- Use Edge functions (faster cold start)

- Enable HTTP caching headers

- Optimize server logic (e.g. reduce DB calls)

1// app/api/route.ts
2export const runtime = 'edge';

Final Thoughts

Optimizing Core Web Vitals in Next.js not only improves technical SEO but also helps boost user trust, engagement, and conversion rates. Combined with open source tools and a performance-first mindset, your Next.js app can outperform the competition.

👉 If you're building a SaaS, eCommerce, or portfolio site in 2025—Core Web Vitals should be your KPI.