A New Measure of User Experience: Core Web Vitals Everyone has likely experienced the frustration of a slow-loading website accessed through an internet search. This inconvenience doesn't merely cause user stress. Slow loading inevitably leads to decreased corporate revenue and lower search engine rankings. In today's increasingly digital economy, this can even result in losses amounting to trillions of won. Many companies worldwide are striving to improve user experience, and at the heart of this effort lies a new standard proposed by Google: 'Core Web Vitals'. Core Web Vitals consist of three key metrics that measure website performance and user experience. These include Interaction to Next Paint (INP), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS). Google first introduced Core Web Vitals in May 2020 and began incorporating them as a ranking factor in its search algorithm from June 2021. These metrics are not merely data analysis tools. By reflecting Core Web Vitals in search rankings through algorithm updates, Google is emphasizing their importance to website owners. This implies that websites not properly optimized risk being left behind in the market. Duda Blog, an American website building platform, has highlighted the necessity of web performance optimization by intensively analyzing data related to Core Web Vitals. According to Duda Blog's analysis, INP and CLS are the metrics currently posing the greatest challenges for websites, with many sites failing to meet recommended standards. Among these, 'slow response times' and 'visual instability' were identified as major issues. For instance, INP measures the time it takes for a user to see the effect on screen after clicking a specific button. According to Google's recommended standards, an INP of less than 200 milliseconds is classified as 'Good,' 200-500 milliseconds as 'Needs Improvement,' and over 500 milliseconds as 'Poor.' A high INP leads to user inconvenience due to slow responses, which can ultimately result in dissatisfaction with the website. Low-quality images, uncompressed videos, and unoptimized fonts exacerbate these problems. LCP is considered the most crucial metric in terms of website loading time. It indicates the time it takes for the largest content element to become visible on the user's screen and can suffer if the website is structurally complex or server response times are slow. Google considers an LCP of under 2.5 seconds as 'Good,' 2.5-4 seconds as 'Needs Improvement,' and over 4 seconds as 'Poor.' Duda Blog emphasizes that "LCP optimization is not just a matter of speed, but about how quickly users can perceive content and begin interacting with it." This can be a serious issue, particularly for business sites like online shopping malls and financial services, which need to elicit immediate user responses. Finally, CLS measures the phenomenon of visual elements shifting on the screen as content loads. A CLS of 0.1 or less is classified as 'Good,' 0.1-0.25 as 'Needs Improvement,' and over 0.25 as 'Poor.' Layout instability can cause misclicks or confuse users, leading them to abandon the website. Three Metrics That Define Website Performance In South Korea, in particular, the importance of Core Web Vitals optimization is growing. While South Korea boasts faster internet speeds than the global average, this has raised user expectations. According to a 2025 survey by the Korea Internet & Security Agency (KISA), the average waiting tolerance time for domestic internet users is approximately 3 seconds; exceeding this leads to a sharp increase in bounce rates. The growing trend of a mobile-centric internet environment further exacerbates this issue. As of 2026, mobile traffic accounts for approximately 75% of total web traffic in South Korea, the highest level among OECD countries. Google's emphasis on mobile-first indexing is also aimed at providing a stable and fast experience for mobile users. However, not all experts accept these criteria as absolute standards. Some developers criticize Core Web Vitals optimization as being overly technology-centric or enforced within Google's monopolistic search engine environment. Web performance expert Tim Kadlec points out on his blog that "Core Web Vitals are useful metrics, but they do not represent the entirety of user experience," arguing that "other important factors such as content quality, accessibility, and security should also be considered." It is true that this makes it difficult for small and medium-sized websites to implement optimization due to limited available resources. These issues are particularly evident in areas like costly image optimization or the demand for advanced server functionalities. Similar concerns are being raised within the domestic web development community. A developer from a small-to-medium enterprise (SME) laments, "Large corporations can have dedicated teams for optimization, but small teams like ours are overwhelmed just by daily
Related Articles