Previously, when adding a new iPhone as a test device, my workflow was to open iTunes, connect the device, click the serial number field on the device summary page to switch it to display the UDID, right-click to copy, and paste that long string of letters and numbers into the developer portal. Every time I switched devices, I had to go through the same tedious process—until I started using a tool that can read it automatically, which made me realize this step didn’t have to be so bothersome. This article walks through the several ways to obtain an iOS device UDID, and also explains what to do after you get it.
What is a UDID
First, let’s clarify what a UDID is. UDID (Unique Device Identifier) is a unique identifier for each iOS device—a 40-character hexadecimal string. It is different from a serial number: the serial number is visible in Settings, while Apple does not directly show the UDID to ordinary users. In development scenarios, its role is very specific: to add a device to the test device list or to allow a device to install your development IPA, you must first obtain the device’s UDID. If the provisioning profile does not contain the target device’s UDID, the compiled package cannot be installed on the phone, and the error prompt will indicate something like “device not authorized” or “device not registered.”
Methods via iTunes and Finder
The most traditional method is using iTunes. Connect your iPhone to the computer, select the device in iTunes, and go to the summary page. By default, it shows the serial number. Click on the serial number text to switch it to the UDID. Right-click to copy the long string. After macOS Catalina, Finder replaced iTunes as the device management location, and the operating logic is the same: select the device in the sidebar, then click the serial number area to toggle the UDID display. Both methods share the same drawback: they rely on Apple’s own tools. On Windows machines without iTunes, you must install it first, and after installation, connection issues are often related to drivers.
Web Page Method
The web page method is suitable when you have the phone at hand and want to skip desktop operations. Using Safari on your phone, open a web page that provides UDID lookup. The page prompts you to install a provisioning profile. Once installed, the web page directly reads and displays the device’s UDID, which you can copy and use. The mechanism is that the web page reads the UDID from device information carried by the provisioning profile. The obtained value is identical to the one from iTunes and can be used to add test devices.
Automatically Reading with Appuploader
If you have Appuploader installed on your computer, obtaining the UDID is even more convenient: just connect your device to the computer via a USB cable, and the tool automatically reads the UDID of the connected device. You don’t need to click around or memorize where the serial number toggle is. Its device management module directly maintains a list of test devices under your account. The read device can be added to the list and synced to your developer account, so you don’t have to switch back and forth between Apple’s website and the tool. For cross-platform teams doing iOS development on Windows, Appuploader can directly read USB devices, eliminating the dependency on iTunes—a particularly handy step.
What to Do After Obtaining the UDID
After obtaining the UDID, the next steps are: log in to the developer portal, register the device under Devices (requires a paid developer account), and then regenerate the provisioning profile—when creating a Development type profile, you must select the test devices. If you don’t select the new device, previously compiled packages still won’t install. In Appuploader, when regenerating the provisioning profile, remember to check this device, then update the signing configuration in your build tool, recompile, and proceed with installation testing.
Troubleshooting Installation Failures
When installation fails, follow this order to check: whether the certificate is a development certificate, whether the provisioning profile includes the target device’s UDID, and whether the device has Developer Mode enabled and trusts the computer. The premise for QR code installation is that the provisioning profile already contains the device’s UDID and the account supports it, while USB installation requires iTunes to be installed, the device unlocked, and the computer trusted.
The several methods for obtaining a UDID differ only in whether you need Apple’s own tools and whether you copy manually. Choose one based on your current environment, and standardize the workflow of “obtain UDID, add test device, regenerate provisioning profile.” From then on, every new device is just a repetition of the same steps.