This is a server that takes a GOPROXY url as an argument and gives you a UI documentation similar to godoc.org except all data comes from the GOPROXY and not from VCS.
For a live demo, see https://moddoc.marwan.io which uses proxy.golang.org
If your GOPROXY supports a /catalog endpoint, then you can see and search the list of existing modules on the home page.
~ GO111MODULE=on go install marwan.io/moddoc
# Assuming you have a GOPROXY server running at http://localhost:3000
~ GOPROXY=http://localhost:3000 moddocVisit http://localhost:3001
You can also visit http://localhost:3001/<module>/@v/<version> to see a documentation package directly.
For example, http://localhost:3001/github.com/pkg/errors/@v/v0.8.1
WIP