Using the OTA Web Updater in the Arduino IDE, this quick instruction shows how to accomplish over-the-air (OTA) programming with the ESP32. The OTA Web Updater allows you to update/upload new code to your ESP32 using a browser without having to connect the ESP32 to your computer through serial.

When you need to update code on ESP32 boards that aren’t easily accessible, OTA programming comes in handy. When the ESP32 and your browser are both on your local network, the example we’ll show below works.

The OTA Web Updater’s main drawback is that you must include the OTA code in every sketch you upload if you want to utilise it in the future.

OTA Web Updater
OTA Web Updater

How does OTA Web Updater Work?

  • The first sketch should be uploaded via serial port. This sketch should contain the code to create the OTA Web Updater, so that you are able to upload code later using your browser.
  • The OTA Web Updater sketch creates a web server you can access to upload a new sketch via web browser.
  • Then, you need to implement OTA routines in every sketch you upload, so that you’re able to do the next updates/uploads over-the-air.
  • If you upload a code without a OTA routine you’ll no longer be able to access the web server and upload a new sketch over-the-air.

ESP32 OTA Web Updater

When you install the ESP32 add-on for the Arduino IDE, it will automatically install the ArduinoOTA library. Go to File > Examples >ArduinoOTA> OTAWebUpdater.


#include <WiFi.h>
#include <WiFiClient.h>
#include <WebServer.h>
#include <ESPmDNS.h>
#include <Update.h>
const char* host = "esp32";
const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";
//variabls to blink without delay:
const int led = 2;
unsigned long previousMillis = 0;        // will store last time LED was updated
const long interval = 1000;           // interval at which to blink (milliseconds)
int ledState = LOW;             // ledState used to set the LED
WebServer server(80);
 * Login page
const char* loginIndex = 
 "<form name='loginForm'>"
    "<table width='20%' bgcolor='A09F9F' align='center'>"
            "<td colspan=2>"
                "<center><font size=4><b>ESP32 Login Page</b></font></center>"
        "<td><input type='text' size=25 name='userid'><br></td>"
            "<td><input type='Password' size=25 name='pwd'><br></td>"
            "<td><input type='submit' onclick='check(this.form)' value='Login'></td>"
    "function check(form)"
    "if(form.userid.value=='admin' && form.pwd.value=='admin')"
    " alert('Error Password or Username')/*displays error message*/"
 * Server Index Page
const char* serverIndex = 
"<script src=''></script>"
"<form method='POST' action='#' enctype='multipart/form-data' id='upload_form'>"
   "<input type='file' name='update'>"
        "<input type='submit' value='Update'>"
 "<div id='prg'>progress: 0%</div>"
  "var form = $('#upload_form')[0];"
  "var data = new FormData(form);"
  " $.ajax({"
  "url: '/update',"
  "type: 'POST',"
  "data: data,"
  "contentType: false,"
  "xhr: function() {"
  "var xhr = new window.XMLHttpRequest();"
  "xhr.upload.addEventListener('progress', function(evt) {"
  "if (evt.lengthComputable) {"
  "var per = evt.loaded /;"
  "$('#prg').html('progress: ' + Math.round(per*100) + '%');"
  "}, false);"
  "return xhr;"
  "success:function(d, s) {"
 "error: function (a, b, c) {"
 * setup function
void setup(void) {
  pinMode(led, OUTPUT);
  // Connect to WiFi network
  WiFi.begin(ssid, password);
  // Wait for connection
  while (WiFi.status() != WL_CONNECTED) {
  Serial.print("Connected to ");
  Serial.print("IP address: ");
  /*use mdns for host name resolution*/
  if (!MDNS.begin(host)) { //http://esp32.local
    Serial.println("Error setting up MDNS responder!");
    while (1) {
  Serial.println("mDNS responder started");
  /*return index page which is stored in serverIndex */
  server.on("/", HTTP_GET, []() {
    server.sendHeader("Connection", "close");
    server.send(200, "text/html", loginIndex);
  server.on("/serverIndex", HTTP_GET, []() {
    server.sendHeader("Connection", "close");
    server.send(200, "text/html", serverIndex);
  /*handling uploading firmware file */
  server.on("/update", HTTP_POST, []() {
    server.sendHeader("Connection", "close");
    server.send(200, "text/plain", (Update.hasError()) ? "FAIL" : "OK");
  }, []() {
    HTTPUpload& upload = server.upload();
    if (upload.status == UPLOAD_FILE_START) {
      Serial.printf("Update: %s\n", upload.filename.c_str());
      if (!Update.begin(UPDATE_SIZE_UNKNOWN)) { //start with max available size
    } else if (upload.status == UPLOAD_FILE_WRITE) {
      /* flashing firmware to ESP*/
      if (Update.write(upload.buf, upload.currentSize) != upload.currentSize) {
    } else if (upload.status == UPLOAD_FILE_END) {
      if (Update.end(true)) { //true to set the size to the current progress
        Serial.printf("Update Success: %u\nRebooting...\n", upload.totalSize);
      } else {
void loop(void) {
  //loop to blink without delay
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) {
    // save the last time you blinked the LED
    previousMillis = currentMillis;
    // if the LED is off turn it on and vice-versa:
    ledState = not(ledState);
    // set the LED with the ledState of the variable:
    digitalWrite(led, ledState);

You should change the following lines on the code to include your own network credentials:

const char* ssid = “”;

const char* password = “”;

The OTAWebUpdater example for the ESP32 develops an asynchronous web server that allows you to update your board’s code without using a serial connection.

The previous code should be uploaded to your ESP32 board. Remember to provide your network credentials and choose the appropriate board and serial port.

After uploading the code, open the Serial Monitor at 115200 baud rate, hit the ESP32 enable button, and the ESP32 IP address should appear:

Now, you can upload code to your ESP32 over the air using a browser on your local network.

To test the OTA Web Updater you can disconnect the ESP32 from your computer and power it using a power bank, for example (this is optional, we’re suggesting this to mimic a situation in which the ESP32 is not connected to your computer).

Update New Code using OTA Web Updater

Open a browser in your network and enter the ESP32 IP address. You should get the following:

Enter the username and the password:

  • Username: admin
  • Password: admin

You can change the username and password on the code.

Preparing the New Sketch

When uploading a new sketch over the air, you need to keep in mind that you need to add code for OTA in your new sketch, so that you can always overwrite any sketch with a new one in the future. So, we recommend that you modify the OTAWebUpdater sketch to include your own code.

For learning purposes let’s upload a new code that blinks an LED (without delay). Copy the following code to your Arduino IDE.

As you can see, we’ve added the “blink without delay” code to the OTAWebUpdater code, so that we’re able to make updates later on.

After copying the code to your Arduino IDE, you should generate a .bin file.

Generate a .bin file in Arduino IDE

Save your sketch as LED_Web_Updater.

To generate a .bin file from your sketch, go to Sketch > Export compiled Binary

A new file on the folder sketch should be created. Go to Sketch > Show Sketch Folder. You should have two files in your Sketch folder: the .ino and the .bin file. You should upload the .bin file using the OTA Web Updater.

Upload a new sketch over the air to the ESP32

In your browser, on the ESP32 OTA Web Updater page, click the Choose File button. Select the .bin file generated previously, and then click Update.

After a few seconds, the code should be successfully uploaded.

The ESP32 built-in LED should be blinking


Over-the-air updates are useful to upload new code to your ESP32 board when it is not easily accessible. The OTA Web Updater code creates a web server that you can access to upload new code to your ESP32 board using a web browser on your local network.

author avatar
Amith G Nair
Experience as a product developer, innovation coach, and electronics lecturer,a seasoned professional driven by passion for designing projects.expertise extends to 3D modelling, hardware designing, and web development using HTML, WordPress, and Django.