diff --git a/convert.rb b/convert.rb
new file mode 100644
index 0000000..46d0393
--- /dev/null
+++ b/convert.rb
@@ -0,0 +1,36 @@
+require "open3"
+require "nokogiri"
+require "net/http"
+require "json"
+
+def render_cached(cache, display, string, render_comment = nil)
+  cache.fetch(string) do |new|
+    puts "  Rendering #{render_comment || new}"
+    res = Net::HTTP.post URI("http://localhost:8000/render"),
+      { :equations => [ { :str => string, :display => display } ] }.to_json,
+       "Content-Type" => "application/json"
+    cache[string] = JSON.parse(res.body)[0]
+  end
+end
+
+def perform_katex_sub(inline_cache, display_cache, content)
+  rendered = content.gsub /\\\(((?:[^\\]|\\[^\)])*)\\\)/ do |match|
+    render_cached(inline_cache, false, $~[1])
+  end
+  rendered = rendered.gsub /\$\$((?:[^\$]|$[^\$])*)\$\$/ do |match|
+    render_cached(display_cache, true, $~[1], "display")
+  end
+  return rendered
+end
+
+files = ARGV[0..-1]
+inline_cache, display_cache = {}, {}
+
+files.each do |file|
+  puts "Rendering file: #{file}"
+  document = Nokogiri::HTML.parse(File.open(file))
+  document.search('//*[not(ancestor-or-self::code)]/text()').each do |t|
+    t.replace(perform_katex_sub(inline_cache, display_cache, t.content))
+  end
+  File.write(file, document.to_html(encoding: 'UTF-8'))
+end
diff --git a/default.nix b/default.nix
index f09ed55..b50bab6 100644
--- a/default.nix
+++ b/default.nix
@@ -1,10 +1,27 @@
-{ bundlerEnv, ruby }:
+{ bundlerEnv, ruby, stdenv }:
 
-bundlerEnv {
-  inherit ruby;
+let
+  env = bundlerEnv {
+    inherit ruby;
 
-  name = "render-test";
-  gemfile = ./Gemfile;
-  lockfile = ./Gemfile.lock;
-  gemset = ./gemset.nix;
-}
+    name = "render-test";
+    gemfile = ./Gemfile;
+    lockfile = ./Gemfile.lock;
+    gemset = ./gemset.nix;
+  };
+in
+  stdenv.mkDerivation {
+    name = "katex-converter";
+    src = ./convert.rb;
+    buildInputs = [ env ruby ];
+    unpackPhase = "echo 'Skipping unpack phase (nothing to unpack)'";
+    installPhase = ''
+      mkdir -p $out/{bin,share/katex-converter}
+      cp $src $out/share/katex-converter/convert.rb
+	cat > $out/bin/katex-converter <<EOF
+#!/bin/sh -e
+exec ${env}/bin/bundle exec ${ruby}/bin/ruby $out/share/katex-converter/convert.rb \$@
+EOF
+      chmod +x $out/bin/katex-converter
+    '';
+  }