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.