diff --git a/tools/proxy.py b/tools/proxy.py
new file mode 100755
index 000000000..0ae571e82
--- /dev/null
+++ b/tools/proxy.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+import http.server, http.client, sys, re
+
+proxyConfig = b'''function FindProxyForURL(url, host) {
+  if (/^http:\/\/s\.4cdn\.org\/(js\/extension\.min\.\d+\.js)?$/.test(url)) {
+    return 'PROXY localhost:8000';
+  }
+  return 'DIRECT';
+}
+'''
+
+class ExtensionReplacer(http.server.BaseHTTPRequestHandler):
+  def do_HEAD(self):
+    self.do_GET()
+
+  def do_GET(self):
+    if self.path == '/proxy.pac':
+      self.send_response(200, 'OK')
+      self.send_header('Content-Length', len(proxyConfig))
+      self.end_headers()
+      if self.command != 'HEAD':
+        self.wfile.write(proxyConfig)
+    elif re.match(r'http://s\.4cdn\.org/js/extension.min.\d+.js$', self.path):
+      self.send_response(302, 'Found')
+      self.send_header('Location', 'https://ccd0.github.io/4chan-x/builds/4chan-X.user.js')
+      self.end_headers()
+    else:
+      conn = http.client.HTTPConnection('s.4cdn.org')
+      conn.request(self.command, self.path, headers=self.headers)
+      response = conn.getresponse()
+      self.send_response(response.status, response.reason)
+      for header, value in response.getheaders():
+        if header not in ('Date', 'Connection'):
+          self.send_header(header, value)
+      self.end_headers()
+      self.wfile.write(response.read())
+      conn.close()
+
+port = int(sys.argv[1]) if 1 < len(sys.argv) else 8000
+httpd = http.server.HTTPServer(('localhost', port), ExtensionReplacer)
+httpd.serve_forever()