DNS Speed Test is a client-side web application that measures DNS-over-HTTPS (DoH) server performance from the user's browser. It implements a single-page architecture with vanilla JavaScript, Tailwind CSS for styling, and Chart.js for data visualization. The core functionality involves building DNS queries, sending them to various DoH endpoints via GET or POST (with CORS handling), measuring round-trip times using performance.now(), and aggregating results into statistics (min, median, average, max). The application stores user preferences (custom hostnames and DoH servers) in localStorage and provides real-time feedback through a responsive UI with sorting, charting, and detailed breakdowns. Key strengths include isolated DNS query construction logic, robust error handling for network timeouts, and a well-tested measurement pipeline. However, the codebase lacks modularity as all logic resides in a single script.js file, limiting reusability without extraction.