gem install json -v 1.7.3 gives 'Please update your PATH to include build tools'

Make sure you install the devkit (ticking the checkboxes that will update the path) :You might need to reinstall ruby too.

Install the DevKit

Download Development Kit from here http://rubyinstaller.org/downloads/

DevKit url at this time For use with Ruby 1.8.7 and 1.9.3: DevKit-tdm-32-4.5.2

For use with Ruby 2.0 and above (32bits version only):DevKit-mingw64-32-4.7.2

For use with Ruby 2.0 and above (x64 - 64bits only)DevKit-mingw64-64-4.7.2

Follow instructions here.

Or short instructions :

Unzip the zip

open command-line and go to unzipped folder

ruby dk.rb init

ruby dk.rb install

gem install rdiscount --platform=ruby

sometimes when you run the ruby dk.rb init you got an error like this

for fixing this problem you have to change the encoding of the command prompt windows .to do this type chcp 1256and you will receive this message : Active code page: 1256

now you can run that command without problem .

good luck .

If you know that you have the proper DevKit installed (eg: via chocolatey), then you simply need to run the included script to set up environment variables.

In cmd:

C:\> d:\path\to\DevKit2\devkitvars.bat

In PowerShell:

PS> . d:\path\to\DevKit2\devkitvars.ps1

These scripts will set up the correct paths in your current command window.