Most sites use a thin slice of nginx: TLS, a folder of static files, a couple of routes to an app, health checks and the odd reload. The config grows anyway, one regex at a time, until nobody is quite sure which block handles a given URL.

BareProxy keeps its core to that slice and makes it answer questions. bareproxy explain takes a URL and shows which rule matched, which file or backend would serve it, and why the rules above it didn’t match. bareproxy why tells the story of a request that already happened, starting from the ID it carried in a response header.