diff --git a/web/app.js b/web/app.js
index b4debf6..6d5711f 100644
--- a/web/app.js
+++ b/web/app.js
@@ -1,5 +1,110 @@
-const $connectButton = document.getElementById('MCU_connect');
+class SerialPortHandler {
+  constructor(options) {
+    this.encoder = new TextEncoder();
+    this.decoder = new TextDecoder();
+    this.options = options;
+    this.port = null;
+    this.writer = null;
+    this.reader = null;
+    this.isOpened = false;
+  }
 
-console.log($connectButton);
+  async open() {
+    if ('serial' in navigator) {
+      try {
+        const port = await navigator.serial.requestPort();
+        await port.open(this.options);
 
-// ...
+        this.port = port;
+        this.writer = port.writable.getWriter();
+        this.reader = port.readable.getReader();
+        this.isOpened = true;
+
+        return this.port.getInfo();
+      } catch (error) {
+        console.error(error);
+        throw error;
+      }
+    } else {
+      console.error('Web Serial API is not supported in your browser.');
+    }
+  }
+
+  async close() {
+    await this.port.close();
+  }
+
+  async write(data) {
+    const encoded = this.encoder.encode(data);
+    return await this.writer.write(encoded);
+  }
+
+  async read() {
+    let data = '';
+    while (true) {
+      const { value, done } = await this.reader.read();
+      if (done) {
+        this.reader.releaseLock();
+        break;
+      }
+      data += this.decoder.decode(value);
+      console.log(data);
+    }
+  }
+}
+
+const $connectButton = document.getElementById('connect');
+const $disconnectButton = document.getElementById('disconnect');
+const $terminalForm = document.getElementById('terminal_form');
+const $serialLog = document.getElementById('serial_log');
+const $status = document.getElementById('status');
+const $vendorId = document.getElementById('vendorId');
+const $productId = document.getElementById('productId');
+
+const serialPortHandler = new SerialPortHandler({ baudRate: 9600 });
+
+async function onConnect() {
+  try {
+    const info = await serialPortHandler.open();
+    console.log('Device connected: ', info);
+    console.log(serialPortHandler.port);
+    $terminalForm.elements.input.removeAttribute('disabled');
+    $vendorId.textContent = '0x' + info.usbVendorId.toString(16);
+    $productId.textContent = '0x' + info.usbProductId.toString(16);
+    $status.textContent = 'CONNECTED';
+  } catch (error) {
+    $status.textContent = 'ERROR';
+  }
+}
+
+async function onDisconnect() {
+  await serialPortHandler.close();
+  $vendorId.textContent = '-';
+  $productId.textContent = '-';
+  $status.textContent = 'NOT CONNECTED';
+}
+
+async function onSend(e) {
+  e.preventDefault();
+  const $form = e.target;
+  const data = $form.elements.input.value;
+  $form.reset();
+  if (serialPortHandler.isOpened) {
+    await serialPortHandler.write(data + '\n');
+    await serialPortHandler.read();
+  }
+}
+
+$connectButton.addEventListener('click', onConnect);
+$disconnectButton.addEventListener('click', onDisconnect);
+$terminalForm.addEventListener('submit', onSend);
+
+// const program1 = setInterval(async () => {
+//   if (serialPortHandler.isOpened) {
+//     await serialPortHandler.write('led_toggle' + '\n');
+//   }
+// }, 50);
+
+// setInterval(() => {
+//   clearInterval(program1);
+// }, 5000);
diff --git a/web/index.html b/web/index.html
index 772b38e..ed0a924 100644
--- a/web/index.html
+++ b/web/index.html
@@ -4,10 +4,39 @@
     <meta charset="UTF-8" />
     <meta http-equiv="X-UA-Compatible" content="IE=edge" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <title>Document</title>
+    <title>Web Serial API Example</title>
+    <link href="./style.css" rel="stylesheet" />
     <script defer src="./app.js"></script>
   </head>
   <body>
-    <button id="MCU_connect">Connect</button>
+    <div class="app">
+      <div>
+        <button id="connect">Connect</button>
+        <button id="disconnect">Disconnect</button>
+      </div>
+      <form id="terminal_form" action="#">
+        <label for="terminal">Enter command name:</label><br />
+        <div class="flex">
+          <input
+            id="input"
+            name="input"
+            placeholder="e.g led_toggle"
+            type="text"
+            disabled
+          />
+          <button type="submit">Send</button>
+        </div>
+      </form>
+      <textarea id="serial_log" placeholder=">" readonly></textarea>
+      <div id="port_info">
+        <div>
+          <p id="status">not connected</p>
+        </div>
+        <div>
+          <span>vendorId: <span id="vendorId">-</span>&nbsp;|</span>
+          <span>deviceId: <span id="productId">-</span></span>
+        </div>
+      </div>
+    </div>
   </body>
 </html>
diff --git a/web/style.css b/web/style.css
new file mode 100644
index 0000000..367913b
--- /dev/null
+++ b/web/style.css
@@ -0,0 +1,93 @@
+:root {
+  --border-color: #c9d1d9;
+  --border-color-hover: #6e7681;
+  --font-family: monospace;
+}
+
+*,
+*:before,
+*:after {
+  box-sizing: inherit;
+}
+
+.app {
+  display: flex;
+  flex-direction: column;
+  /* padding: 20px; */
+  width: 100%;
+  max-width: 600px;
+  row-gap: 5px;
+}
+
+html,
+body {
+  box-sizing: border-box;
+  font-size: 16px;
+}
+
+body {
+  display: flex;
+  justify-content: center;
+  margin-top: 2rem;
+  font-family: var(--font-family);
+}
+
+p {
+  padding: 0;
+  margin: 5px;
+}
+
+input,
+textarea {
+  font-family: var(--font-family);
+  padding: 5px 15px;
+  border-radius: 4px;
+  width: 100%;
+  border: 1px solid var(--border-color);
+}
+
+textarea {
+  resize: vertical;
+  min-height: 200px;
+  font-size: 16px;
+  outline: none;
+  font-size: 12px;
+}
+
+label {
+  font-size: 14px;
+  font-style: italic;
+}
+
+button {
+  cursor: pointer;
+  background: none;
+  font-family: var(--font-family);
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  padding: 5px 15px;
+}
+
+button:hover {
+  border: 1px solid var(--border-color-hover);
+}
+
+#terminal_form div {
+  display: flex;
+  justify-content: space-between;
+  gap: 5px;
+  margin-bottom: 5px;
+  margin-top: 5px;
+}
+
+#port_info {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  flex-wrap: wrap;
+  font-size: 14px;
+}
+
+#port_info #status {
+  text-transform: uppercase;
+}