HAD is GHC's devs companion tool. It is meant to be run in GHC's sources root directory.
Install it with:
> git clone https://github.com/hsyl20/had.git
> cd had
> stack install
Be sure that the path where stack has installed "had" (e.g., ~/.local/bin) is in your PATH.
To use it:
> cd ghc_home_directory
> had -p 6789
Then navigate to "http://localhost:6789"