link rel="dns-prefetch" is a lightweight front-end optimization method that is suitable for scenarios where pages refer to multiple third-party resources or CDNs. When a webpage uses external resources such as Google Fonts, statistics scripts, alliance JS, or multiple CDN domain names, you can reduce the DNS query time by resolving the domain name in advance. The correct way to use it is to add: <link rel="dns-prefetch" href="//example.com"> in the HTML, but it should avoid abuse and give priority to domain names that must be loaded later. The difference between it and preconnect is that the latter also establishes TCP and TLS connections. The two can be used in combination, in order first dns-prefetch and then preconnect. Other points of attention include no need to add to the main site, more obvious mobile effects, and limited support for testing tools. Rational use can bring stable performance improvements.
To put it directly into the key point: link rel="dns-prefetch"
is a lightweight but easily overlooked front-end optimization method, especially suitable for scenarios where the page refers to multiple third-party resources or CDNs.

When should I use dns-prefetch
If your webpage refers to external resources, such as Google Fonts, statistics scripts, ad alliance JS, or uses multiple CDN domains to distribute static files, you can consider adding this tag.
DNS resolution is the first step in a browser to load a page, and the resolution is usually initiated before requesting a resource. Through dns-prefetch
, you can tell the browser in advance: "I will use these domain names later, please help me resolve them first." This way, when you really need to load, you can save the time of a DNS query.

Common applicable scenarios:
- The page references multiple resources with different domain names
- Public CDNs are used (such as fonts.gstatic.com, cdn.jsdelivr.net)
- There are many third-party plug-ins, such as comment system, sharing button, and burying scripts
How to use it correctly
The usage is very simple, just add a line of code similar to the following in the area of HTML:

<link rel="dns-prefetch" href="//example.com">
Pay attention to some details:
- The protocol part can be omitted, and it is more common to start with
//
- Don't abuse it, too much will increase the burden on the browser
- Priority is given to setting pre-parses for domain names that "it will only be loaded later but must be used"
For example, if you use Google Fonts, you can add a line to the head:
<link rel="dns-prefetch" href="//fonts.gstatic.com">
In this way, the browser will parse the domain name in advance when it is idle, speeding up the font loading speed.
Differences from preconnect
Many people will confuse dns-prefetch
and preconnect
. In fact, although they are all optimization methods, they do different things:
-
dns-prefetch
does only one thing: parse the IP corresponding to the domain name in advance -
preconnect
goes a step further, not only does DNS resolution, but also establishes TCP connections and even TLS handshakes.
So if you are sure that a domain name will be used soon, it will be better to directly use preconnect
. But if it is just "maybe used", it is safer to use dns-prefetch
.
The two can be used together, generally the order is dns-prefetch
first and then preconnect
:
<link rel="dns-prefetch" href="//example.com">
Some points that are easy to ignore
- Don't add to the current main site : the browser has automatically done DNS resolution of the main site, and adding it will be unnecessary
- Mobile terminals are more effective : In mobile network environment, DNS resolution delay is much higher than that of desktop, and early processing can improve the experience
- Test tool support is limited : Some performance analysis tools do not specifically indicate whether dns-prefetch is effective, and can only observe the DNS search for reduction through the timeline.
Basically that's it. It doesn't seem complicated, but in actual projects, especially on multi-resource loading pages, reasonable use can indeed bring a small but stable optimization effect.
The above is the detailed content of HTML `link rel='dns-prefetch'` Optimization. For more information, please follow other related articles on the PHP Chinese website!

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