Next.js Core Web Vitals Optimization: Ship Lighthouse 100 Pages
We engineer Next.js sites that pass every Core Web Vitals threshold
Your Current Site May Be a Liability
Common gaps we find in nearly every audit.
Honestly, "undefined" isn't much to work with -- and that's putting it kindly
Risk: So let me just say this: when your data comes back as undefined, something broke upstream. Maybe a prop didn't get passed, maybe an API returned null, maybe someone forgot to initialize a variable. It happens to everyone. I've seen it tank production deployments at 2am more times than I'd like to admit. Here's the thing -- undefined in JavaScript means a variable exists but has no assigned value. That's different from null, which is an intentional absence. Different from an empty string. Different from zero. Undefined is the language saying "I know this thing exists, but nobody told me what it is yet." In React, it shows up constantly -- undefined components, undefined props, undefined API responses that you forgot to handle. And in Next.js specifically, you'll hit it when getServerSideProps or getStaticProps returns data your component isn't expecting. The fix is usually straightforward: add a default value, add a conditional check, or trace the data flow back to where it broke. Nine times out of ten, it's a missing fallback.
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Purpose-built features for your industry.
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Social Animal
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Get a free quoteFrequently Asked Questions
A properly optimised Next.js site should hit LCP under 2.5 seconds, CLS under 0.1, and INP under 200ms. And honestly? With server components and Vercel Edge deployment, those aren't stretch goals -- hitting Lighthouse 95-100 on mobile is genuinely realistic. Our production sites consistently score 98-100 on desktop and 90-100 on mobile. Not cherry-picked results. Consistent ones.
The usual suspects: client-side JavaScript blocking LCP -- swap those out for server components instead. Layout shift from dynamic content or fonts loading late gets fixed with next/font, which is pretty straightforward to drop in. Slow INP from heavy React hydration is trickier but solvable by reducing client components. And unoptimised images are low-hanging fruit -- just use next/image with the priority flag on your LCP element.
For an existing Next.js site, a focused CWV engagement typically runs 2-4 weeks. We start with a diagnostic audit -- usually 3-5 days -- then move into fixes for 1-2 weeks, and verify everything against real field data from CrUX. Here's the thing about timelines: Lighthouse improvements show up within days. But CrUX field data takes 28 days to update, so don't panic if Search Console lags behind what you're seeing locally.
Yes. Google confirmed CWV as a ranking signal back in 2021 and it's only carried more weight since. Pages that fail CWV thresholds get deprioritised in mobile search results -- that's not speculation, it's documented. But the real kicker? Poor CWV correlates directly with bounce rate. Every 100ms of additional load time costs measurable conversions. So this isn't just an SEO issue. It's a revenue issue.
Yes -- and this is actually most of what we do. Social Animal specialises in retrofitting CWV optimisation onto existing Next.js applications. We're not going to ask you to rewrite your app. We audit your current scores, find the 3-5 changes that actually move the needle, and in most cases we're talking 30+ point improvements without touching your core architecture. If you're sitting on a Next.js site with a Lighthouse score in the 60s, there's almost certainly a faster path forward than you think.
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