# Can you send me your UDID? My what???

> What a UDID is, why app developers ask for it before you can test an app, how to find yours with Finder, Xcode or Windows, and how TestFlight avoids it.

By Koen Van Looveren, impaktfull · Published 2025-01-06

Source: https://www.impaktfull.com/blog/can-you-send-me-your-udid

You are about to test an app, and the developer asks: "Can you send me your UDID?" Your what? Here is what a UDID is, why developers ask for it, and how to find yours in a minute.

**The fastest way:** connect your iPhone to a Mac, open Finder, select it, click the grey line under its name until the UDID appears, then right-click and choose Copy UDID. No computer at hand? [Use your iPhone itself](#on-your-iphone-itself-without-a-computer).

## What is a UDID?

The UDID (Unique Device Identifier) is a long code that identifies one specific iPhone, iPad or Mac. On recent iPhones it looks like `00008110-001A2B3C4D5E6F70`; on older ones it is 40 characters long.

## Why does a developer need it?

Apple only lets an app run on devices it trusts. An app that doesn't come from the App Store or TestFlight, like a test build, has to be signed with a provisioning profile that lists the devices it may run on. That list is made of UDIDs. So before you can install a test build, the developer registers your UDID in their Apple Developer account and makes a new build.

A developer account can register up to 100 devices per device type (iPhone, iPad, Mac, ...) per membership year. Disabling a device during the year doesn't free its place; the list can only be cleaned up when a new membership year starts, so developers are careful with it.

## How to find your UDID

### With a Mac (Finder)

1. Connect your iPhone or iPad to your Mac with a cable, and trust the computer if your device asks.
2. Open Finder and select your device in the sidebar.
3. Click the grey line under the device's name (with the model and storage) until it shows the UDID.
4. Right-click it and choose **Copy UDID**.

### With Xcode

Connect your device, open **Window → Devices and Simulators**, and copy the **Identifier**.

### With Windows

In the Apple Devices app (or iTunes), select your device and click the serial number until it shows the UDID.

### On your iPhone itself, without a computer

You won't find the UDID in the Settings app of your iPhone: Apple doesn't show it there. But a website can ask for it, with a profile you install. We built one for this: [appstore.impaktfull.com/udid](https://appstore.impaktfull.com/udid/).

1. Open the page in Safari on your iPhone or iPad and tap the button.
2. Allow the profile to download, then install it in Settings (General → VPN & Device Management).
3. You return to the page, which shows your UDID: copy it and share it with your development team.

The profile only reads your device's details; it doesn't change anything on your device. Still, only install profiles from websites you trust, like one your developer recommends.

## Testing without a UDID: TestFlight

There is an easier way for most testers. With [TestFlight](https://developer.apple.com/testflight/), Apple's own beta app, a developer invites you by email or link; you install TestFlight and the app, and no UDID is needed. A team can have up to 100 internal testers and up to 10,000 external testers per app, and the first build you share with external testers is reviewed by Apple.

A UDID still makes sense for builds that can't go through TestFlight, like an internal app that is installed from a website.

Getting test builds to your team or client without the back and forth? We set up [test and release flows](https://www.impaktfull.com/service/apps) for every app we build.

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impaktfull builds and runs apps, websites, platforms and AI agents, from Antwerp, Belgium. More at https://www.impaktfull.com.