Before
Japanese web fonts are large. A single Noto Sans JP or Hiragino-fallback web font file can weigh 2MB to 10MB uncompressed, covering the full Unicode CJK range. When a site loads a CJK web font without subsetting to the characters actually used on the page, it is downloading a font file orders of magnitude larger than necessary. Font subsetting, combined with the unicode-range CSS descriptor to load only the character ranges needed per page, is the single highest-impact performance intervention available on most Japanese sites. It directly improves both Largest Contentful Paint and First Contentful Paint.
After
CJK font subsetting is the highest-impact intervention available on most Japanese sites. When a 4MB unsubsetted CJK font file is replaced with a 40KB subsetted font loading only the characters on that page, the browser receives the font data far earlier in the load sequence. This directly reduces First Contentful Paint and Largest Contentful Paint in both lab and field data. For sites where CJK fonts were the primary LCP bottleneck, the score change is substantial.
Before
Japanese site designs frequently use large, high-quality photography, particularly in the hospitality, real estate, and consumer goods sectors. These images are often served as large JPEGs without conversion to WebP or AVIF, without proper compression, and without preload hints that would allow the browser to fetch them at high priority early in the page load. A 1.2MB hero image served without modern encoding is a reliable LCP failure, regardless of the speed of the underlying network.
After
The performance gap between desktop and mobile on Japanese sites is often wider than the raw network difference would suggest. Mobile CPUs process large JavaScript bundles more slowly than desktop CPUs. When JavaScript is audited and reduced, INP and Time to Interactive improve specifically on mobile devices. Japanese users on mid-range Android hardware, which represents a significant share of mobile browsing in Japan, experience this improvement directly.
Before
Many Japanese sites that have been actively developed for five or more years carry JavaScript debt. Tag manager containers with outdated or unused tags, jQuery plus a more recent framework loaded simultaneously, tracking scripts for platforms that are no longer in use, and feature code from discontinued functionality. This accumulated JavaScript loads on every page, blocks the main thread, and directly degrades Interaction to Next Paint. The fix requires a structured audit, not a search for a plugin.
After
For Japanese companies whose English-language site is performing poorly in CrUX field data for US, UK, or Australian users, fixing the performance issues removes a disadvantage in international search results. International visitors who previously arrived and left quickly because the page was slow now experience a site that loads correctly for their device and connection.
Before
Some smaller Japanese sites are still served directly from origin servers. Others have a CDN in place but with default cache settings that are not appropriate for the site's asset types. For international-facing Japanese sites, CDN edge node selection for the target market, such as US or European points of presence, is often not configured. The result is avoidable latency for every international visitor.
After
Without monitoring, performance degradation is discovered at the next audit, often months later. With monitoring in place, new images added without proper compression, new scripts introduced through a tag manager, or font loading regressions are visible in Google Search Console data as they occur. The monitoring configuration we implement gives ongoing visibility without requiring manual checks.
