diff --git a/service_worker.ts b/service_worker.ts
new file mode 100644
index 0000000..4289388
--- /dev/null
+++ b/service_worker.ts
@@ -0,0 +1,50 @@
+/**
+ *  @license
+ *   Copyright 2018 Google LLC
+ *
+ *   Licensed under the Apache License, Version 2.0 (the "License");
+ *   you may not use this file except in compliance with the License.
+ *   You may obtain a copy of the License at
+ *
+ *       https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *   Unless required by applicable law or agreed to in writing, software
+ *   distributed under the License is distributed on an "AS IS" BASIS,
+ *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *   See the License for the specific language governing permissions and
+ *   limitations under the License.
+ */
+
+// This listener is called when the user clicks the extension icon.
+
+// If the current URL matches a Jupyter notebook hosted on github.com
+// or on gist.github.com, this function will open a new tab and load
+// the notebook into Colab.
+
+chrome.action.onClicked.addListener((tab: chrome.tabs.Tab) => {
+  const colab_url = 'https://colab.research.google.com/';
+  const github = /^https?:\/\/github\.com\/(.+)\/(.*\.ipynb)$/;
+  const gist =
+      /^https?:\/\/gist\.github\.com\/(.+)\/([a-f0-9]+(?:\#file\-.*\-ipynb)?)$/;
+
+  if (!tab.url) {
+    console.warn('Open in Colab was invoked without a URL.');
+    return;
+  }
+
+  let url = null;
+
+  const githubPath = github.exec(tab.url);
+  const gistPath = gist.exec(tab.url);
+  if (githubPath) {
+    url = colab_url + ['github', githubPath[1], githubPath[2]].join('/');
+  } else if (gistPath) {
+    url = colab_url + ['gist', gistPath[1], gistPath[2]].join('/');
+  }
+
+  if (url) {
+    chrome.tabs.create({'url': url});
+  } else {
+    console.warn(`Current page (${tab.url}) is not recognized as a GitHub-hosted notebook.`);
+  }
+});