User Agent

In web accessibility, a user agent is any software that retrieves, renders, and facilitates user interaction with web content. This includes mainstream web browsers like Chrome, Firefox, and Safari, as well as assistive technologies such as screen readers that work alongside browsers. User agents play a critical role in the accessibility chain: they must support content reflow for different viewport sizes, expose semantic information to accessibility APIs, navigate form structures, and honor user preferences for text size, color, and interaction mode. The User Agent Accessibility Guidelines (UAAG) 2.0 specifies how user agents should support accessibility both through their own interfaces and through communication with assistive technologies. Because accessibility features implemented at the user agent level need only be built once per browser rather than once per website, user agent support represents the most cost-effective layer for systemic accessibility improvements.