Registering UDID: The Key to iOS App Testing

To test an iOS app outside the App Store and TestFlight, each tester's iPhone or iPad must be registered with Apple by its UDID (Unique Device Identifier). You add the UDID to your Apple Developer account, include the device in an Ad Hoc or Development provisioning profile, rebuild the app with that profile, and then the build installs on that device. This guide covers what a UDID is, how to find it, how to register it, and the limits to plan for.

What is a UDID?

A UDID is a unique identifier Apple assigns to each iPhone, iPad and other Apple device. Older devices use a 40 character hexadecimal string. Newer devices, starting around the iPhone XS generation, use a 25 character format with a hyphen after the first 8 characters, for example 00008030-001A2B3C4D5E6F70.

Apple uses the UDID to decide which devices may run a build that did not come from the App Store or TestFlight. A provisioning profile lists the allowed UDIDs, and iOS refuses to install the app on any device not in the list.

When you need to register a UDID

How the build is distributed	UDID registration needed?
Development build (from Xcode or shared)	Yes
Ad Hoc build (shared by link or file)	Yes
TestFlight	No, testers are invited by email or public link
App Store	No
Enterprise (Apple Developer Enterprise Program, employees only)	No

So UDIDs matter when you want quick testing on a small set of known devices without App Store review, which is the most common case for sharing builds by link.

How to find a device's UDID

With the AppForShare UDID finder (on the iPhone, no computer)

1. On the iPhone, open appforshare.io/udid in Safari.
2. Allow the download of the configuration profile, then open Settings and install it when prompted.
3. You are returned to a page that shows the UDID, plus details such as model, iOS version and serial number, depending on what iOS returns.
4. Copy it, email it to the developer, or save it to your AppForShare account.

The UDID finder is free and needs no account. AppForShare deletes UDID lookups after 1 day. A step by step walkthrough with screenshots is in how to find the UDID on an iPhone.

With a Mac

• Finder (macOS Catalina and later): connect the iPhone with a cable, select it in the Finder sidebar, then click the line of text under the device name until the UDID appears. Right click to copy it.
• Xcode: open Window, then Devices and Simulators, select the connected device and copy the Identifier.

Older guides mention iTunes. On current macOS, iTunes has been replaced by Finder for device management.

How to register a UDID with Apple

1. Sign in to your Apple Developer account and open Certificates, Identifiers and Profiles.
2. Go to Devices and click the add button.
3. Choose the platform, enter a recognisable device name (for example "Sara iPhone 15") and paste the UDID. You can also upload a file to register several devices at once.
4. Go to Profiles, open your Ad Hoc (or Development) profile, and make sure the new device is selected. Save to regenerate the profile.
5. In Xcode, download the updated profile (or let automatic signing refresh it), archive the app again and export it with the Ad Hoc method.
6. Upload the new .ipa and share the link. Builds made before the device was added will still not install on it.

That last point catches many teams: registering the UDID is not enough on its own. The build must be signed with a profile that includes the device. AppForShare does not re-sign builds, so the new build has to come from your Xcode or CI pipeline.

Limits and common problems

• Device limit: Apple allows up to 100 registered devices per device type (for example iPhone, iPad) per membership year. Removing a device does not free its slot until your membership renews, so register carefully.
• Typos: a single wrong character means the device is not in the profile. Copy and paste, or use the UDID finder, rather than typing.
• Expired profile or certificate: provisioning profiles and distribution certificates expire. When they do, builds signed with them stop installing or launching. Check expiry dates before a test round.
• "Unable to install" on the iPhone: usually the device is not in the profile, or the build was made before it was added. See can't install an app on an iOS device.
• Developer Mode: on iOS 16 and later, development signed builds need Developer Mode turned on. See how to enable Developer Mode on iPhone.

Tips for managing UDIDs

• Use clear device names in the Apple portal that include the owner and model.
• Keep a simple list of who owns which device and which profiles include it.
• Collect UDIDs before a test round, register them in one batch, and build once.
• If you need more testers than the device limit allows, use TestFlight for the wider group and keep Ad Hoc for the core team.

Privacy

A UDID identifies a specific device, so treat it as personal data: only collect it from people who agreed to test, store it only where you need it, and delete it when the device is no longer used. The AppForShare UDID finder keeps lookups for 1 day only, unless the user saves the device to their own account. See the privacy policy for details.

Frequently asked questions

What is a UDID and why does iOS testing need it?

A UDID is a unique identifier for each Apple device. Ad Hoc and Development builds only install on devices whose UDID is in the provisioning profile, so testers' UDIDs must be registered before they can install a build shared by link.

How can I find my iPhone's UDID?

Open appforshare.io/udid in Safari on the iPhone and install the profile it offers, which shows your UDID. On a Mac, you can also connect the iPhone and read the UDID in Finder or in Xcode under Devices and Simulators.

I registered the UDID, so why will the app still not install?

The build must be signed with a provisioning profile that includes the device. Regenerate the Ad Hoc profile with the new device selected, rebuild and export the app, and share the new build.

How many devices can I register with Apple?

Apple allows up to 100 devices per device type, such as iPhone or iPad, per membership year. Removed devices only free up their slot when the membership renews.

Do I need UDIDs for TestFlight or Enterprise builds?

No. TestFlight invites testers by email or public link, and Enterprise builds are signed for an organization's employees without device registration. UDIDs are needed for Ad Hoc and Development builds.