diff --git a/extension/api/go-webserial-native-msg.js b/extension/api/go-webserial-native-msg.js
new file mode 100644
index 0000000..6a25e40
--- /dev/null
+++ b/extension/api/go-webserial-native-msg.js
@@ -0,0 +1,216 @@
+'use strict';
+
+var NMSerialPort;
+NMSerialPort = {
+    openPromises: new Map(),
+
+    addPromise: function(eventName, promise)
+    {
+        if (NMSerialPort.openPromises.has(eventName))
+        {
+            var promises = NMSerialPort.openPromises.get(eventName);
+            promises.push(promise);
+            NMSerialPort.openPromises.set(eventName, promises);
+        }
+        else
+        {
+            NMSerialPort.openPromises.set(eventName, [promise]);
+        }        
+    },
+
+    sendMessage: function(message)
+    {
+        window.postMessage({ type: "togws", message: message }, "*");
+    },
+
+    handleSerialPortsEvent: function(message)
+    {
+        var promises = NMSerialPort.openPromises.get(message.event);
+        if (promises)
+        {
+            for (var i = 0; i < promises.length; i++)
+            {
+                if (promises[i].filters)
+                {
+                    promises[i].resolve(SerialPort.filterPorts(message.data, promises[i].filters));
+                }
+                else
+                {
+                    promises[i].resolve(message.data);
+                }
+            }
+            NMSerialPort.openPromises.delete(message.event)
+        }
+    },
+
+    handleSerialPortOpened: function(message)
+    {
+        var promises = NMSerialPort.openPromises.get(message.event);
+        if (promises)
+        {
+            for (var i = 0; i < promises.length; i++)
+            {
+                if (promises[i].devicePath == message.devicePath)
+                {
+                    promises[i].object.id = message.id;
+                    NMSerialPort.openObjects.push(promises[i].object);
+
+                    promises[i].resolve(message.data);
+                }
+            }
+            NMSerialPort.openPromises.delete(message.event)
+        }        
+    },
+
+    handleData: function(message)
+    {
+        // Decode data into typed array
+        var decodedString = atob(message.data)
+        var uint8Array = new Uint8Array(decodedString.length);
+        for (var i = 0; i < decodedString.length; i++)
+        {
+            uint8Array[i] = decodedString.charCodeAt(i);
+        }
+
+        // Find and call the relevant callback
+        for (i = 0; i < NMSerialPort.openObjects.length; i++)
+        {
+            if (NMSerialPort.openObjects[i].id == message.id)
+            {
+                NMSerialPort.openObjects[i].callback(uint8Array);
+                break;
+            }
+        }
+    },
+
+    handleSerialPortClosed: function(message)
+    {
+        // Find the relevant object and change its state
+        for (var i = 0; i < NMSerialPort.openObjects.length; i++)
+        {
+            if (NMSerialPort.openObjects[i].id == message.id)
+            {
+                NMSerialPort.openObjects[i].id = -1;
+                if (NMSerialPort.openObjects[i].onCloseCallback)
+                {
+                    NMSerialPort.openObjects[i].onCloseCallback();
+                }
+                NMSerialPort.openObjects.splice(i, 1);
+                break;
+            }
+        }        
+    },
+
+    onWindowEvent: function(event)
+    {
+
+        // Communication with the content script
+
+        // We only accept messages from this window with type set to fromgws
+        if (event.source != window || event.data.type != "fromgws")
+            return;
+        var message = event.data.message
+        if (message.event)
+        {
+            switch (message.event)
+            {
+                case "SerialPorts":
+                NMSerialPort.handleSerialPortsEvent(message);
+                break;
+
+                case "PortOpen":
+                NMSerialPort.handleSerialPortOpened(message);
+                break;
+
+                case "data":
+                NMSerialPort.handleData(message);
+                break;
+
+                case "PortClosed":
+                NMSerialPort.handleSerialPortClosed(message);
+                break;
+            }
+
+        }
+    },
+
+    openObjects: [] // open serial port objects
+};
+
+window.addEventListener("message", NMSerialPort.onWindowEvent);
+
+class SerialPort {
+    constructor(devicePath, modeOptions) {
+        console.log("Creating a serial connection to ", devicePath);
+        this.devicePath = devicePath;
+        this.modeString = "";
+        this.id = -1;
+        if(modeOptions) {
+            for(var key in modeOptions) {
+                this.modeString += "&" + key + "=" + modeOptions[key];
+            }
+        }
+    }
+
+    static requestPorts(filters) {
+        return new Promise(function(resolve, reject) {
+            NMSerialPort.addPromise("SerialPorts", {resolve: resolve, reject: reject, filters: filters});
+
+            NMSerialPort.sendMessage({command: "listPorts"});
+        });
+    }
+
+    static filterPorts(portList, filters) {
+        var result = [];
+
+        portList.forEach( function(port) {
+            var idx, filter;
+            for(idx = 0; idx < filters.length; idx++) {
+                filter = filters[idx];
+                for(var key in filter) {
+                    if(port[key] !== filter[key]) {
+                        return;
+                    }
+                }
+            }
+            result.push(port);
+        });
+
+        return result;
+    }
+
+    set onClose(callback) {
+        this.onCloseCallback = callback;
+    }
+
+    connect(callback) {
+        this.callback = callback;
+        return new Promise(function(resolve, reject) {
+            NMSerialPort.addPromise("PortOpen", {resolve: resolve, reject: reject, object: this, devicePath: this.devicePath});
+
+            NMSerialPort.sendMessage({ command: "open", devicePath: this.devicePath, baudRate: 57600 });
+        }.bind(this));
+    }
+
+    disconnect() {
+        if (this.id != -1)
+        {
+            NMSerialPort.sendMessage({command: "close", id: this.id});
+        }
+    }
+
+    write(data) {
+        if (this.id != -1)
+        {
+            // Convert data (ArrayBuffer format) to base64 string
+            var uint8Array = new Uint8Array(data);
+            var string = "";
+            for (var i = 0; i < uint8Array.length; i++)
+            {
+                string += String.fromCharCode(uint8Array[i]);
+            }
+
+            NMSerialPort.sendMessage({command: "write", id: this.id, data: btoa(string)})
+        }
+    }
+}