diff --git a/LICENSE b/LICENSE
index 7bcaec7..e6acb8c 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,5 @@
-Copyright (c) 2009 Eric Kidd
+sinatra-url-for - Construct absolute paths and full URLs
+Copyright 2009 Eric Kidd
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
diff --git a/README.rdoc b/README.rdoc
index dc4db51..2a213ce 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -1,7 +1,27 @@
 = sinatra-url-for
 
-Description goes here.
+<code>sinatra-url-for</code> can be used by a Sinatra application to
+construct absolute paths and full URLs.  For example:
+
+  gem 'emk-sinatra-url-for'
+  require 'sinatra/url_for'
+
+  # From within a request.
+  url_for "/"            # Returns "/myapp/"
+  url_for "/foo"         # Returns "/myapp/foo"
+  url_for "/foo", :full  # Returns "http://example.com/myapp/foo"
+
+If you're subclassing <code>Sinatra::Base</code>, then you need to call
+<code>helpers</code> manually:
+
+  class MyApp < Sinatra::Base
+    helpers Sinatra::UrlForHelper
+    # ...
+  end
+
+Thanks to "cypher23" on #mephisto and the folks on #rack for pointing me in
+the right direction.
 
 == Copyright
 
-Copyright (c) 2009 Eric Kidd. See LICENSE for details.
+Copyright 2009 Eric Kidd. See LICENSE for details.
diff --git a/lib/sinatra/url_for.rb b/lib/sinatra/url_for.rb
new file mode 100644
index 0000000..3dfa1dd
--- /dev/null
+++ b/lib/sinatra/url_for.rb
@@ -0,0 +1,37 @@
+module Sinatra
+  module UrlForHelper
+    # Construct a link to +url_fragment+, which should be given relative to
+    # the base of this Sinatra app.  The mode should be either
+    # <code>:path_only</code>, which will generate an absolute path within
+    # the current domain (the default), or <code>:full</code>, which will
+    # include the site name and port number.  (The latter is typically
+    # necessary for links in RSS feeds.)  Example usage:
+    #
+    #   url_for "/"            # Returns "/myapp/"
+    #   url_for "/foo"         # Returns "/myapp/foo"
+    #   url_for "/foo", :full  # Returns "http://example.com/myapp/foo"
+    #--
+    # See README.rdoc for a list of some of the people who helped me clean
+    # up earlier versions of this code.
+    def url_for url_fragment, mode=:path_only
+      case mode
+      when :path_only
+        base = request.script_name
+      when :full
+        scheme = request.scheme
+        if (scheme == 'http' && request.port == 80 ||
+            scheme == 'https' && request.port == 443)
+          port = ""
+        else
+          port = ":#{request.port}"
+        end
+        base = "#{scheme}://#{request.host}#{port}#{request.script_name}"
+      else
+        raise TypeError, "Unknown url_for mode #{mode}"
+      end
+      "#{base}#{url_fragment}"
+    end
+  end
+
+  helpers UrlForHelper
+end
diff --git a/lib/sinatra_url_for.rb b/lib/sinatra_url_for.rb
deleted file mode 100644
index e69de29..0000000
diff --git a/spec/sinatra_url_for_spec.rb b/spec/sinatra_url_for_spec.rb
deleted file mode 100644
index f79c1a2..0000000
--- a/spec/sinatra_url_for_spec.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-require 'spec_helper'
-
-describe "SinatraUrlFor" do
-  it "fails" do
-    fail "hey buddy, you should probably rename this file and start specing for real"
-  end
-end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 6e65ef0..fe4e321 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,8 +1,8 @@
+require 'rubygems'
 require 'spec'
 
 $LOAD_PATH.unshift(File.dirname(__FILE__))
 $LOAD_PATH.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
-require 'sinatra_url_for'
 
 Spec::Runner.configure do |config|
   
diff --git a/spec/url_for_spec.rb b/spec/url_for_spec.rb
new file mode 100644
index 0000000..e9e7754
--- /dev/null
+++ b/spec/url_for_spec.rb
@@ -0,0 +1,26 @@
+require 'spec_helper'
+require 'sinatra'
+require 'sinatra/test'
+require 'sinatra/url_for'
+
+get "/" do
+  content_type "text/plain"
+  <<"EOD"
+#{url_for("/")}
+#{url_for("/foo")}
+#{url_for("/foo", :full)}
+EOD
+end
+
+describe Sinatra::UrlForHelper do
+  include Sinatra::Test
+  it "should return absolute paths and full URLs" do
+    get "/"
+    response.should be_ok
+    response.body.should == <<EOD
+/
+/foo
+http://example.org/foo
+EOD
+  end
+end