DNS Prefetching
Causality Engine TeamTL;DR: What is DNS Prefetching?
DNS Prefetching dNS Prefetching is a browser optimization technique that resolves domain names before a user clicks a link. This reduces latency by speeding up DNS lookup times, contributing to faster page navigation and improved web performance.
DNS Prefetching
DNS Prefetching is a browser optimization technique that resolves domain names before a user clicks ...
Causality EngineWhat is DNS Prefetching?
DNS Prefetching is a browser optimization technique designed to reduce latency by resolving domain names before the user initiates a request to those domains. When a user clicks a link, the browser normally performs a DNS (Domain Name System) lookup to translate the domain name into an IP address, which can introduce delays ranging from 20 milliseconds to several hundred milliseconds depending on network conditions. DNS Prefetching proactively performs this lookup for anticipated external domains, allowing subsequent requests to complete faster since the DNS resolution step has already been done. This technique was introduced as part of web performance optimizations in the early 2010s and is now widely supported by modern browsers through the use of the <link rel="dns-prefetch" href="//example.com"> HTML tag or HTTP headers such as "X-DNS-Prefetch-Control". In the context of e-commerce, DNS Prefetching is particularly valuable because online stores often rely on resources hosted across multiple domains—like content delivery networks (CDNs), third-party analytics scripts, payment gateways, or marketing platforms. For example, a Shopify fashion retailer may load images from a CDN domain, tracking pixels from advertising platforms, and payment processing from a third-party domain. By prefetching DNS for these domains, the website reduces page load times and improves the overall user experience, which is critical to minimizing bounce rates and increasing conversion rates. On a technical level, the browser stores the DNS resolution in its cache so when the user clicks through or when scripts request resources, the network stack bypasses the DNS lookup step entirely. DNS Prefetching complements other web performance techniques like preconnect and prerendering but is lower cost and simpler to implement, making it a common best practice for performance-conscious e-commerce sites.
Why DNS Prefetching Matters for E-commerce
For e-commerce marketers, every millisecond of page load time matters. Studies consistently show that faster websites yield higher conversion rates; for instance, a 100-millisecond improvement can increase conversion rates by up to 7% according to Google research. DNS Prefetching directly contributes to faster page navigation by reducing the DNS lookup latency involved when loading external assets or redirecting users to checkout and payment systems. This improvement can lead to higher sales and lower cart abandonment rates. Moreover, in today’s competitive e-commerce landscape, optimizing web performance is a key differentiator. Brands that implement DNS Prefetching alongside comprehensive attribution platforms like Causality Engine can more accurately measure the impact of performance optimizations on customer behavior and ROI, using causal inference methods to isolate the effect of faster load times on conversions. Additionally, faster navigation enhances user experience on mobile devices, where network latency is often higher, further expanding the reach and satisfaction of online shoppers.
How to Use DNS Prefetching
Implementing DNS Prefetching involves identifying the external domains your e-commerce site interacts with, such as CDNs, advertising platforms, payment gateways, and analytics services. First, audit your site’s network requests using tools like Chrome DevTools or Lighthouse to list all third-party domains. Next, add <link rel="dns-prefetch" href="//example.com"> tags in the <head> section of your HTML for each domain you want to pre-resolve. For example, a Shopify beauty brand might prefetch domains like //cdn.shopify.com, //google-analytics.com, and //stripe.com. Alternatively, configure HTTP response headers to include "X-DNS-Prefetch-Control: on" if you want to enable DNS Prefetching globally. Test the implementation by comparing page load metrics before and after using performance monitoring tools such as Google PageSpeed Insights or WebPageTest. Combine DNS Prefetching with other optimizations like preconnect or prefetch for resource hints to further improve load times. Finally, leverage Causality Engine’s attribution analytics to measure how the improvements in performance, including DNS Prefetching, causally drive better user engagement and sales outcomes.
Industry Benchmarks
- description
- Typical DNS lookup times vary between 20-120 milliseconds on broadband connections, but can exceed 200 milliseconds on mobile networks. Effective DNS Prefetching can reduce these lookup times close to zero for prefetched domains, contributing to overall page load time improvements of 2-10% on average for complex e-commerce sites. According to Google, reducing page load time by 100ms can increase conversion rates by up to 7%.
- sources
- Google Web Fundamentals: https://web.dev/dns-prefetch/,Google Research on Mobile Speed Impact: https://www.thinkwithgoogle.com/marketing-resources/data-measurement/mobile-page-speed-new-industry-benchmarks/,Chrome DevTools Documentation: https://developer.chrome.com/docs/devtools/
Common Mistakes to Avoid
Prefetching too many domains: Overusing DNS Prefetching for unnecessary or rarely used domains can waste bandwidth and browser resources, potentially slowing down the critical page load path. Prioritize domains critical to user navigation and conversion.
Ignoring mobile users: Mobile networks have higher latency; failing to implement DNS Prefetching on mobile-optimized sites misses a key opportunity to reduce delays for mobile shoppers.
Not testing impact: Implementing DNS Prefetching without validating performance improvements through tools like Lighthouse or Causality Engine’s causal analysis can lead to misattributed or negligible gains.
Using DNS Prefetching instead of preconnect: DNS Prefetching only resolves DNS, while preconnect also establishes TCP and TLS handshakes. For domains critical to initial page load, preconnect might be more effective.
Neglecting security implications: Prefetching domains without proper consideration can lead to privacy or security risks if those domains are untrusted or serve malicious content. Always verify third-party domains.