Getting set up to use webdev takes some time, if you're doing anything more than tweaking a bit of text. Here are the initial setup steps:

$ mkdir site  
$ cd site  
$ git clone [email protected]:dart-lang/site-webdev.git  
$ source ./scripts/env-set.sh  
$ ./scripts/install-dart-sdk.sh  
$ ./scripts/before-install.sh  
$ rvm install 2.3.0  
$ ./scripts/install.sh  
$ ./scripts/get-ng-repo.sh

For more details, see one of our Travis builds.