Localhost request lifecycle in Next.js development shows the complete journey from user input through app rendering. The browser resolves localhost to 127.0.0.1, establishes a TCP handshake with the Next.js dev server, sends an HTTP GET request, and receives HTML, JavaScript, and CSS. The server matches the route, renders React components, and builds the response while the browser parses the response, constructs the DOM, and hydrates React to display the final app. This flow demonstrates how local development differs from production by eliminating DNS resolution and using direct loopback addressing. Fork this diagram to customize it for your own Next.js architecture documentation or learning materials.