diff --git a/manifest.json b/manifest.json
index 1e340f71..da2e2b44 100644
--- a/manifest.json
+++ b/manifest.json
@@ -22,7 +22,7 @@
 		"downloads"
 	],
 	"background": {
-		"scripts": ["messaging.js", "storage-websql.js", "storage.js", "background.js"]
+		"scripts": ["messaging.js", "storage-websql.js", "storage.js", "background.js", "update.js"]
 	},
 	"commands": {
 	  "openManage": {
diff --git a/update.js b/update.js
new file mode 100644
index 00000000..29adf508
--- /dev/null
+++ b/update.js
@@ -0,0 +1,84 @@
+/* globals getStyles, saveStyle */
+'use strict';
+
+var update = {
+  fetch: (resource, callback) => {
+    let req = new XMLHttpRequest();
+    let [url, data] = resource.split('?');
+    req.open('POST', url, true);
+    req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
+    req.onload = () => callback(req.responseText);
+    req.onerror = req.ontimeout = () => callback();
+    req.send(data);
+  },
+  md5Check: (style, callback) => {
+    let req = new XMLHttpRequest();
+    req.open('GET', style.md5Url, true);
+    req.onload = () => {
+      let md5 = req.responseText;
+      if (md5 && md5 !== style.originalMd5) {
+        callback(style);
+      }
+      else {
+        console.log(`"${style.name}" style is up-to-date`);
+      }
+    };
+    req.onerror = req.ontimeout = () => console.log('Error validating MD5 checksum');
+    req.send();
+  },
+  list: (callback) => {
+    getStyles({}, (styles) => callback(styles.filter(style => style.updateUrl)));
+  },
+  perform: () => {
+    // from install.js
+    function arraysAreEqual (a, b) {
+      // treat empty array and undefined as equivalent
+      if (typeof a === 'undefined') {
+        return (typeof b === 'undefined') || (b.length === 0);
+      }
+      if (typeof b === 'undefined') {
+        return (typeof a === 'undefined') || (a.length === 0);
+      }
+      if (a.length !== b.length) {
+        return false;
+      }
+      return a.every(function (entry) {
+        return b.indexOf(entry) !== -1;
+      });
+    }
+    // from install.js
+    function sectionsAreEqual(a, b) {
+      if (a.code !== b.code) {
+        return false;
+      }
+      return ['urls', 'urlPrefixes', 'domains', 'regexps'].every(function (attribute) {
+        return arraysAreEqual(a[attribute], b[attribute]);
+      });
+    }
+
+    update.list(styles => {
+      styles.forEach(style => update.md5Check(style, style => update.fetch(style.updateUrl, response => {
+        if (response) {
+          let json = JSON.parse(response);
+
+          if (json.sections.length === style.sections.length) {
+            if (json.sections.every((section) => {
+              return style.sections.some(installedSection => sectionsAreEqual(section, installedSection));
+            })) {
+              return console.log('everything is the same');
+            }
+            json.method = 'saveStyle';
+            json.id = style.id;
+
+            saveStyle(json, function () {
+              console.log(`"${style.name}" style is updated`);
+            });
+          }
+          else {
+            console.log('style sections mismatch');
+          }
+        }
+      })));
+    });
+  }
+};