diff --git a/README.md b/README.md
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+++ b/README.md
@@ -0,0 +1,9 @@
+Net Speed
+=========
+
+Show current net speed on panel.
+--------------------------------
+
+This extension is inspired by <https://github.com/biji/simplenetspeed/> which has some annoying flickers existing for a long time so I decide to create my own alternative. I removed all features that I won't use.
+
+It only shows text like `↓ 777 K/s ↑ 2.33 K/s` on the right part of panel. No font size changing, no total downloaded bytes, no bits.
diff --git a/extension.js b/extension.js
new file mode 100644
index 0000000..2c95df7
--- /dev/null
+++ b/extension.js
@@ -0,0 +1,211 @@
+/* extension.js
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+/* exported init */
+
+// const GETTEXT_DOMAIN = "net-speed";
+
+const {GObject, GLib, Gio, Clutter, St} = imports.gi;
+
+// const Gettext = imports.gettext.domain(GETTEXT_DOMAIN);
+// const _ = Gettext.gettext;
+
+const ByteArray = imports.byteArray;
+const ExtensionUtils = imports.misc.extensionUtils;
+const Main = imports.ui.main;
+const PanelMenu = imports.ui.panelMenu;
+// const PopupMenu = imports.ui.popupMenu;
+
+const refreshInterval = 3;
+const speedUnits = [
+    "B/s", "K/s", "M/s", "G/s", "T/s", "P/s", "E/s", "Z/s", "Y/s"
+];
+let lastTotalDownBytes = 0;
+let lastTotalUpBytes = 0;
+
+const getCurrentNetSpeed = (refreshInterval) => {
+    const speed = {"down": 0, "up": 0};
+
+    try {
+        const inputFile = Gio.File.new_for_path("/proc/net/dev");
+        const fileInputStream = inputFile.read(null);
+        // See <https://gjs.guide/guides/gobject/basics.html#gobject-construction>.
+        // If we want new operator, we need to pass params in object.
+        // Short param is only used for static constructor.
+        const dataInputStream = new Gio.DataInputStream({
+            "base_stream": fileInputStream
+        });
+
+        // Caculate the sum of all interfaces' traffic line by line.
+        let totalDownBytes = 0;
+        let totalUpBytes = 0;
+        let line = null;
+        // See <https://gjs-docs.gnome.org/gio20~2.66p/gio.datainputstream#method-read_line>.
+        while ((line = dataInputStream.read_line(null)) != null) {
+            // See <https://github.com/GNOME/gjs/blob/master/doc/ByteArray.md#tostringauint8array-encodingstringstring>.
+            // It seems Uint8Array is only returned at the first time.
+            if (line instanceof Uint8Array) {
+                line = ByteArray.toString(line).trim();
+            } else {
+                line = line.toString().trim();
+            }
+            const fields = line.split(/\W+/);
+            if (fields.length <= 2) {
+                break;
+            }
+
+            // Skip virtual interfaces.
+            const interface = fields[0];
+            const currentInterfaceDownBytes = Number.parseInt(fields[1]);
+            const currentInterfaceUpBytes = Number.parseInt(fields[9]);
+            if (interface == "lo" ||
+                // Created by python-based bandwidth manager "traffictoll".
+                interface.match(/^ifb[0-9]+/) ||
+                // Created by lxd container manager.
+                interface.match(/^lxdbr[0-9]+/) ||
+                interface.match(/^virbr[0-9]+/) ||
+                interface.match(/^br[0-9]+/) ||
+                interface.match(/^vnet[0-9]+/) ||
+                interface.match(/^tun[0-9]+/) ||
+                interface.match(/^tap[0-9]+/) ||
+                isNaN(currentInterfaceDownBytes) ||
+                isNaN(currentInterfaceUpBytes)) {
+                continue;
+            }
+
+            totalDownBytes += currentInterfaceDownBytes;
+            totalUpBytes += currentInterfaceUpBytes;
+        }
+
+        fileInputStream.close(null);
+
+        if (lastTotalDownBytes === 0) {
+            lastTotalDownBytes = totalDownBytes;
+        }
+        if (lastTotalUpBytes === 0) {
+            lastTotalUpBytes = totalUpBytes;
+        }
+
+        speed["down"] = (totalDownBytes - lastTotalDownBytes) / refreshInterval;
+        speed["up"] = (totalUpBytes - lastTotalUpBytes) / refreshInterval;
+
+        lastTotalDownBytes = totalDownBytes;
+        lastTotalUpBytes = totalUpBytes;
+    } catch (e) {
+        logError(e);
+    }
+
+    return speed;
+};
+
+const formatSpeedWithUnit = (amount) => {
+    let unitIndex = 0;
+    while (amount >= 1000 && unitIndex < speedUnits.length - 1) {
+        amount /= 1000;
+        ++unitIndex;
+    }
+
+    let digits = 0;
+    // Instead of showing 0.00123456 as 0.00, show it as 0.
+    if (amount >= 100 || amount - 0 < 0.01) {
+        // 100 M/s, 200 K/s, 300 B/s.
+        digits = 0;
+    } else if (amount >= 10) {
+        // 10.1 M/s, 20.2 K/s, 30.3 B/s.
+        digits = 1;
+    } else {
+        // 1.01 M/s, 2.02 K/s, 3.03 B/s.
+        digits = 2;
+    }
+
+    // See <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed>.
+    return `${amount.toFixed(digits)} ${speedUnits[unitIndex]}`;
+};
+
+const toSpeedString = (speed) => {
+    return `↓ ${formatSpeedWithUnit(speed["down"])} ↑ ${formatSpeedWithUnit(speed["up"])}`;
+};
+
+const Indicator = GObject.registerClass(
+class Indicator extends PanelMenu.Button {
+    _init() {
+        // menuAlignment, nameText, dontCreateMenu.
+        super._init(0.0, "Net Speed", true);
+
+        this._label = new St.Label({
+            "y_align": Clutter.ActorAlign.CENTER,
+            "text": "---"
+        });
+
+        this.add_child(this._label);
+
+        // let item = new PopupMenu.PopupMenuItem(_("Show Notification"));
+        // item.connect("activate", () => {
+        //     Main.notify(_("Whatʼs up, folks?"));
+        // });
+        // this.menu.addMenuItem(item);
+    }
+
+    setText(text) {
+        return this._label.set_text(text);
+    }
+});
+
+class Extension {
+    constructor(uuid) {
+        this._uuid = uuid;
+
+        // ExtensionUtils.initTranslations(GETTEXT_DOMAIN);
+    }
+
+    enable() {
+        lastTotalDownBytes = 0;
+        lastTotalUpBytes = 0;
+
+        this._indicator = new Indicator();
+        // role, indicator, position, box.
+        // -1 is not OK, because it will show in the right side of system menu.
+        Main.panel.addToStatusArea(this._uuid, this._indicator, 0, "right");
+
+        this._timeout = GLib.timeout_add_seconds(
+            GLib.PRIORITY_DEFAULT, refreshInterval, () => {
+                const speed = getCurrentNetSpeed(refreshInterval);
+                const text = toSpeedString(speed);
+                // log(text);
+                this._indicator.setText(text);
+                // Run as loop, not once.
+                return GLib.SOURCE_CONTINUE;
+            }
+        )
+    }
+
+    disable() {
+        if (this._indicator != null) {
+            this._indicator.destroy();
+            this._indicator = null;
+        }
+        if (this._timeout != null) {
+            GLib.source_remove(this._timeout);
+            this._timeout = null;
+        }
+    }
+}
+
+function init(meta) {
+    return new Extension(meta.uuid);
+}
diff --git a/metadata.json b/metadata.json
new file mode 100644
index 0000000..052b081
--- /dev/null
+++ b/metadata.json
@@ -0,0 +1,9 @@
+{
+  "name": "Net Speed",
+  "description": "Show current net speed on panel.",
+  "uuid": "netspeed@alynx.one",
+  "version": 1,
+  "shell-version": [
+    "40"
+  ]
+}
diff --git a/stylesheet.css b/stylesheet.css
new file mode 100644
index 0000000..37b93f2
--- /dev/null
+++ b/stylesheet.css
@@ -0,0 +1 @@
+/* Add your custom extension styling here */