After install Jekyll, I had to do a bundle install (not mentioned in the doc, is that normal?), and then:

$ jekyll server -w --config _config.yml,_config_local.yml
WARN: Unresolved specs during Gem::Specification.reset:
      jekyll-watch (~> 1.1)
WARN: Clearing out unresolved specs.
Please report a bug if this causes problems.
Configuration file: _config.yml
Configuration file: _config_local.yml
       Deprecation: The 'pygments' configuration option has been renamed to 'highlighter'. Please update your config file accordingly. The allowed values are 'rouge', 'pygments' or null.
       Deprecation: You appear to have pagination turned on, but you haven't included the `jekyll-paginate` gem. Ensure you have `gems: [jekyll-paginate]` in your configuration file.
  Dependency Error: Yikes! It looks like you don't have kramdown or one of its dependencies installed. In order to use Jekyll as currently configured, you'll need to install this gem. The full error message from Ruby is: 'cannot load such file -- kramdown' If you run into trouble, you can find helpful resources at http://jekyllrb.com/help/!
jekyll 3.1.3 | Error:  kramdown

I'm not very familiar with Jekyll and I understand some errors. However, I think the repo needs a lil' update code and/or documentation wise for allowing people to contribute to it.

The content on http://www.phpmetrics.org/documentation/configuration.html is outdated.
Now the settings file can be a *.ini or *.json file so also the example is outdated.
I discovered that only reading the code of the tool and the unit tests.

Please NEVER change any CSS file manually. You should use the less files contained in ./less directory.

Where is the ./less directory?

website is not working

although make it working via gh-pages proposed url phpmetrics.github.io should work aswell if there is any problem with dns, or the domain itself

Visiting http://www.phpmetrics.org/documentation/plugins-extensions.html from the left hand menu gives a 404.

Might have been introduced by 97f8717 where the page name was changed, but no corresponding change in menu happened.

Would it be possible to remove the www subdomain? I guess it's a question of personal taste, but I always felt like www was completely unnecessary and got in the way.