Background: In today’s digital era, the internet plays a pervasive role in our lives, influencing everyday activities such as communication, work, and leisure. This online engagement intertwines with offline experiences, shaping individuals’ overall well-being. Despite its significance, existing research often falls short in capturing the relationship between internet use and wellbeing, relying primarily on isolated studies and self-reported data. One major contributor to deteriorated wellbeing is stress. While some research has examined the relationship between internet use and stress, both positive and negative associations have been reported. Objective: Our primary goal in this work is to identify the associations between an individual’s internet use and their stress. Methods: We conducted a seven-month longitudinal study. We combined fine-grained URL-level web browsing traces of 1490 German internet users with their sociodemographics and monthly measures of stress. Further, we developed a conceptual framework that allows us to simultaneously explore different contextual dimensions, including how, where, when, and by whom the internet is used. We applied linear mixed models to examine these associations. Results: Our analysis revealed several associations between internet use and stress, varying by context. Increased time spent on social media, online shopping, and gaming platforms was associated with higher stress. For example, the time spent by individuals on shopping-related internet use (aggregated over the 30 days before their stress was measured via questionnaires) was positively associated with stress on both mobile (β = 0.04, CI = [0.00–0.08], P = .035) and desktop devices (β = 0.03, CI = [-0.00–0.06], P = .090). In contrast, time spent on productivity or news websites was associated with lower stress. Specifically, in the last 30 days of mobile usage, productivity-related use showed a negative association with stress (β = -0.03, CI = [-0.06– -0.00], P = .042). Additionally, in the last two days of data, news usage was negatively associated with stress on both mobile (β = -0.54, CI = [-1.08–0.00], P = .048) and desktop devices (β = -0.50, CI = [-0.90– -0.11], P = .012). Further analysis showed that total time spent online (β = 0.01, CI = [0.00–0.02], P 26) individuals on mobile devices. Conclusions: The findings indicate that internet use is associated with stress, and these associations differ across various usage contexts. In the future, the behavioral markers we identified can pave the way for designing individualized tools for people to self-monitor and self-moderate their online behaviors to enhance their well-being, reducing the burden on already overburdened mental health services.