To optimize LCP, you need to start from four aspects: image resources, server response, render blocking resources and preload management. 1. Image optimization includes using WebP/AVIF format, setting srcset and sizes, compressing sizes and delaying loading non-first-screen images; 2. Improve server response speed can be achieved through CDN, HTTP/2 or 3 and optimizing back-end interface performance; 3. Optimizing JS/CSS, delaying non-critical scripts, inline key CSS and deleting redundant code; 4. Use link preload to preload key resources, optimize font loading and adjust resource priorities, thereby accelerating content presentation and improving user experience and SEO performance.

Largest Contentful Paint (LCP) is an important metric for measuring web page loading experience, which directly affects user experience and search engine rankings. Optimizing LCP can not only make your website perceived by users faster, but also improve SEO performance. The following are some practical and practical optimization directions.

Image resource optimization: Reduce loading time

Images are usually one of the main sources of LCP elements, and optimizing them can significantly improve LCP performance.

• Use modern image formats : such as WebP or AVIF, which are smaller in size at the same image quality.
• Responsive image settings : Through srcset and sizes attributes, let the browser choose the appropriate image size according to the device.
• Compressed image size : Do not upload images that exceed the required size of the page, such as an image with a display of 300x200, there is no need to use the original image of 1920x1080.
• Lazy loading of non-first-screen images : Although LCP focuses on the content of the first screen, avoiding loading of non-key images can free up bandwidth to more important resources.

For example, a picture that does not properly set up srcset may load too large files on a high-resolution device, resulting in a few seconds of LCP delay, which is an issue that is easy to ignore but has a big impact.

Server response speed: shorten first rendering time

The starting point of LCP time is calculated from the user opening the page, so the faster the server responds, the better.

• Use CDN to accelerate static resources : put pictures, JS, CSS and other files on nodes close to the user to speed up the transmission speed.
• Enable HTTP/2 or HTTP/3 : These protocols support multiplexing to reduce request latency.
• Optimize back-end performance : Slow database query and complex interface processing will slow down the rendering of the first screen, which will affect LCP.

If your homepage interface requires more than 500ms to return data, then this time will be directly included in the overall time-consuming of LCP and must be taken seriously.

Render blocking resource optimization: render content as early as possible

JavaScript and CSS are common render blocking resources, and too many or unoptimized scripts can affect LCP.

• Split and lazy load JS : JS with non-critical functions can be lazy loaded or used defer and async properties.
• Inline key CSS : Write the styles required by the first screen directly into HTML to avoid additional requests.
• Remove unused CSS and JS : Tools such as PurgeCSS can help clean up redundant styles.

For example, if your page starts rendering the main content after loading a bunch of JS, then the LCP will be severely delayed. The content part should be loaded and rendered first.

Using preloading and priority management: Actively control the loading order

The default loading order of the browser is not necessarily the best. You can interfere with resource loading priorities through some means.

• Use <link rel="preload"> to preload key resources : such as LCP images, fonts, and key JS/CSS.
• Font optimization : Slow font loading will affect text display. Use font-display: swap to let text be displayed in default font first.
• Adjust resource priority : Prompt the browser through HTTP headers or HTML tags which resources are more important.

For example, you can add:

 <link rel="preload" as="image" href="hero.jpg">

In this way, the browser knows that this image is very important and should be loaded first.

Basically these common optimization points. LCP seems to be an indicator, but in fact, the content loading, server response, rendering process and other links involved are not complicated but are easy to ignore details.

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