gem install caldecott ERROR: While executing gem ... (Gem::FilePermissionError) You don't have write permissions for the /Users/spencer/.rvm/gems/ruby-2.0.0-p0 directory. ~ spencer$ caldecott -bash: caldecott: command not found ~ spencer$ af tunnel To use `af tunnel', you must first install Caldecott:
gem install caldecott
Note that you'll need a C compiler. If you're on OS X, Xcode will provide one. If you're on Windows, try DevKit.