Computed once, or every time

The last piece of the picture is *when* code runs. A page whose output is identical for every visitor can be rendered once, when the project is built, and served as a finished file forever after. A page whose output depends on the request (who is logged in, which problem was asked for) must be rendered per request. This is static versus dynamic renderingWhether a page's HTML is computed once at build time or freshly on every request., and it is the same trade as precomputing a lookup table versus evaluating a function on demand: cheaper per use, but only valid when the answer does not vary. Next.js decides this per route and prints the verdict in the build output. A circle marks a static route, an f marks a dynamic one. Reading that output is the quickest way to catch a page that has accidentally become dynamic and is now doing work on every single visit.