dns-prefetch improves loading speed by resolving external domain names in advance. Specifically, it allows the browser to parse the DNS of third-party resources when it is idle, reducing the delay in subsequent requests. Suitable for references to multi-domain static resources, key third-party services, and links that users may click on. Abuse should be avoided during use, priority should be given to key resources, and can be used with preconnect. For example: Add dns-prefetch to Google Analytics and CDN, while key resources such as fonts are more efficient with preconnect.
Web page loading speed is particularly important for both user experience and SEO, and <link rel="dns-prefetch">
is a simple but easily overlooked point in the optimization process. It can help the browser resolve the domain names of external resources in advance, thereby reducing the delay in subsequent requests.

What is dns-prefetch
?
Simply put, dns-prefetch
is a technology that allows browsers to perform DNS resolution in advance when they are idle. We know that visiting a website requires first converting the domain name into an IP address through DNS, which will cause certain delays. If multiple third-party resources are referenced in the page (such as Google Fonts, statistics scripts, etc.), this delay will accumulate.
It is also very straightforward to use:

<link rel="dns-prefetch" href="//example.com">
After writing this way, the browser will quietly parse the DNS of example.com in the background, and save time for a DNS query when it really needs to load resources.
Which situations are suitable for using dns-prefetch
?
Not all external links need pre-parsing, and these scenarios are given priority:

- The page refers to static resources from different domains, such as fonts, pictures, and scripts.
- Third-party services have a direct impact on page functions or styles, such as maps, comment systems, and advertising spaces.
- Users may prepare for that page in advance before clicking on a link (advanced usage).
For example: If you use Google Analytics and Cloudflare CDNs, you can write this:
<link rel="dns-prefetch" href="//www.google-analytics.com"> <link rel="dns-prefetch" href="//cdn.example.com">
This way the browser can prepare information about these domain names earlier.
Things to pay attention to when using
Although dns-prefetch is lightweight, there are some details to pay attention to:
- Don't abuse it, just target external domain names that really need to be used.
- It is not recommended to add too many unimportant domain names, otherwise resources may be wasted.
- Some preload strategies (such as
preconnect
) are more comprehensive than it, but also have more overhead.
For example, if you just load a very small icon and the source domain name is not a performance bottleneck, there is actually no need to add it. In contrast, it is very meaningful to parse key resources like font files in advance.
In addition, dns-prefetch
can be used with preconnect
. If you are sure to load resources from a domain name, it is more efficient to use preconnect
directly:
<link rel="preconnect" href="//fonts.gstatic.com" crossorigin>
But we will discuss this topic later.
Basically that's it. Although it is small, in overall performance optimization, every small improvement can accumulate into more.
The above is the detailed content of HTML `link rel='dns-prefetch'` for Performance. For more information, please follow other related articles on the PHP Chinese website!

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