If you have a remote host that has some JSON data you need you can very quickly and easily proxy that host's response using Sinatra. This is useful for local development. There are other ways to do this of course, but in a pinch the following solution works, albeit without error handling.

#./server.rb  
require 'net/http'

HOST = 'example.com'

get "/package/details.json/:id" do  
  content_type "application/json"
  uri = URI::HTTP.build(
        :host  => HOST, 
        :path  => "/package/details.json/#{params[:id]}",
        :query => 'some_parameter=abc'
  )
  Net::HTTP.get(uri)
end

get "/simulate/details.json/:device_identifier" do  
  content_type "application/json"
  uri = URI::HTTP.build(
    :host => HOST,
    :path => "/simulate/details.json/#{params[:device_identifier]}"
  )
  Net::HTTP.get(uri)
end