Core Web Vitals are a set of three specific web speed and user interaction metrics that Google uses as direct SEO ranking factors. For single-page applications (SPAs) built with React, Vue, or Angular, maintaining high scores is particularly challenging due to heavy client-side JavaScript execution and layout shifts.
Providing a fast page speed is essential. If your pages take more than 3 seconds to load or shift layouts as resources load, search engines will downgrade your position in search listings.
The Three Core Web Vitals Metrics
Optimize your website performance around these three core measurements:
1. Largest Contentful Paint (LCP)
LCP measures loading performance. Specifically, it marks the time it takes to render the largest visible text block or image on the screen. * **Good Score:** Under 2.5 seconds. * **SPA optimization:** Pre-load hero images, server-side render content (SSR), and defer non-critical JS.
2. Interaction to Next Paint (INP)
INP replaced First Input Delay (FID) as a core metric, measuring website responsiveness. It tracks the delay of all user interactions (clicks, key presses) during the entire page session. * **Good Score:** Under 200 milliseconds. * **SPA optimization:** Avoid blocking the main thread with long JavaScript loops, use web workers, and defer state transitions.
3. Cumulative Layout Shift (CLS)
CLS measures visual stability. It quantifies how much elements move or jump around as the page loads content. * **Good Score:** Under 0.1. * **SPA optimization:** Always declare explicit size dimensions (width/height attributes) on image and video tags, and reserve space for dynamic ads.
Audit Your Technical Speed
Are layout shifts or heavy scripts dragging down your rankings? Run a technical performance check to optimize speed blocks.
Run Core Web Vitals Audit →