The psql -h pg.neon.tech command is a feature in Neon that allows users to connect to their projects without needing passwords. When run, it generates a URL that takes the user to a UI where they can choose which project or endpoint to connect to. This command is useful for developers working with multiple Neon projects or endpoints, as it simplifies the connection process and eliminates the need to remember URLs or credentials. The "Link Proxy" service running in the data plane generates this URL and initiates a connection to the correct IP with appropriate credentials. Both the regular Neon Proxy and the "Link Proxy" are open source, allowing users to explore their codebase and ask questions about their architecture on Neon's Discord server.