GitHub prioritizes responsiveness in web application design, with speed being a crucial element, and employs various internal tools to monitor and improve performance metrics. The performance dashboard, powered by data from Graphite, provides an overview of response times across different types of requests but lacks detailed explanations. To address this, GitHub uses the Mission Control Bar in staff mode, providing a detailed breakdown of time periods for rendered pages, which helps identify slowness from the network, browser, or application. This tool displays application metrics such as compressed javascript and CSS sizes, background job queues, and data source times, allowing for in-depth analysis. GitHub also integrates additional tools like New Relic and Graphite to enhance performance investigations, with the overarching goal of delivering an exceptionally fast web application.