How GOV.UK Removed jQuery and Measured Its Performance Impact

In March, Matt Hobbs, the front‑end lead for GOV.UK, announced that the site would drop jQuery as a dependency for all front‑end applications, a move later explained in detail by senior front‑end engineer Andy Sellick.

GOV.UK, the UK government’s online portal, must work for all users regardless of device or connection speed, prompting the team to continuously seek performance and user‑experience improvements.

The site consists mainly of static pages with JavaScript used for analytics, cookies, and small UI interactions; jQuery was widely used, especially for Ajax, but its inclusion added about 32 KB to the average 246 KB homepage, slowing load times.

Rather than upgrading to a newer jQuery version, the team decided to remove it entirely, involving both front‑end and back‑end developers who received training to undertake the task.

After the removal, the team observed that eliminating the 32 KB compressed JavaScript could significantly benefit users on low‑spec devices, which often struggle with JavaScript’s blocking nature during rendering.

Performance tests using simulated low‑end devices and 2G connections showed that visual completion time for the most‑visited “Universal Credit” page dropped from 11.3 seconds to 9.4 seconds (a 17 % improvement), total page load time fell from 20.42 seconds to 18.75 seconds (8 % faster), and interaction metrics such as First CPU Idle improved by 17 %.

Real‑User Monitoring data indicated that 75 % of users are in the UK, 35 % use Android devices, and the first pixel often appears after about 2 seconds, confirming many users are on low‑performance hardware.

The article concludes that while jQuery remains widely used (over 34 % of sites according to Wappalyzer), removing it can be essential for extreme performance optimization, especially for content‑heavy sites like GOV.UK.