Developer Mode on iPhone: When Scarlet iOS and Sideloaded Apps Need It
Developer Mode is a setting Apple added in iOS 16. It decides whether your iPhone will run apps signed with a developer certificate, which is exactly how tools like AltStore and Sideloadly install apps. Whether you need it depends on how an app was signed, not on which app you want. This guide explains when Developer Mode is required, when it is not (including for Scarlet iOS), and how to turn it on and off safely.
Note: Scarlet iOS does not have its own in-app Developer Mode. Everything below is about Apple’s system setting in iOS. Last checked: October 27, 2026, against Apple’s Xcode documentation on enabling Developer Mode.
The Short Version
- Scarlet itself does not need Developer Mode. It is enterprise-signed, so you trust its profile in Settings instead.
- Developer Mode is for apps signed with your own Apple ID: SideStore, AltStore, Sideloadly and Xcode.
- Apple warns that turning it on “reduces the security of your device”. Turn it off again when you no longer use those tools.
Which Installs Need Developer Mode?
| How the app got on your iPhone | Signed with | Developer Mode |
|---|---|---|
| App Store | Apple | Not needed |
| TestFlight | Apple | Not needed |
| Scarlet iOS | Enterprise certificate | Not needed (trust the profile instead) |
| SideStore, AltStore, Sideloadly | Your Apple ID (development certificate) | Needed on iOS 16 and later |
| Xcode, or an .ipa installed with Apple Configurator | Development certificate | Needed on iOS 16 and later |
What Developer Mode Does
Since iOS 16, an iPhone refuses to launch apps signed with a development certificate unless Developer Mode is on. Development certificates are what you get from an Apple ID, free or paid, when a tool signs an app for your own devices. Apple added the switch so that this kind of app cannot run on a phone by accident; turning it on is a deliberate choice that requires a restart.
Apps from the App Store, TestFlight, and apps distributed with an enterprise certificate are not affected by this setting.
In Apple’s developer documentation, Developer Mode is described as a guard against installing harmful software by accident and a way to keep developer-only features closed off on ordinary phones. Apple also explains that it leaves normal installs alone, such as App Store purchases and TestFlight betas. What it covers is running an app built in Xcode, or putting an .ipa file on the device with Apple Configurator. Sideloading tools that sign with your Apple ID produce the same kind of development-signed app, so the same rule applies to them.
When You Need Developer Mode
- AltStore (classic) with your Apple ID: AltStore and the apps it installs are signed with your personal development certificate, so on iOS 16 and later they will not open until Developer Mode is on.
- Sideloadly: apps signed with your Apple ID through Sideloadly need Developer Mode on iOS 16 and later for the same reason. See our Sideloadly guide.
- SideStore: it signs apps with your own Apple ID too, so SideStore and its apps need Developer Mode. Setup steps are in our SideStore guide.
- Xcode builds: if you build and run your own app from Xcode, Developer Mode is required.
- Any tool that signs with your own developer certificate: if the app was signed with your Apple ID or developer account, expect to need it.
If you are on iOS 15 or earlier, the setting does not exist and is not needed.
When You Do Not Need It: Scarlet iOS
Scarlet iOS installs apps signed with an enterprise-style certificate rather than your personal development certificate. For those apps, iOS asks for a different step: you trust the developer profile once in Settings, General, VPN and Device Management. Developer Mode is not part of that process.
So if Scarlet or an app installed with it will not open, Developer Mode is usually not the fix. Check these instead:
- The profile has not been trusted yet: see how to fix the Untrusted Developer error.
- The certificate has been revoked by Apple: see what to do when the Scarlet certificate is revoked.
- You see an “Unable to Verify App” message: see how to fix Unable to Verify App.
Turning Developer Mode on does no harm to Scarlet, but it does not make enterprise-signed apps work any better.
How to Turn On Developer Mode (iOS 16 and Later)
- Install the app that needs it first (for example AltStore or an app from Sideloadly). According to Apple, the Developer Mode option shows up in Settings only after the iPhone has started pairing with a Mac or was paired with one before; in practice it also shows up once a developer-signed app is on the iPhone.
- Open Settings and tap Privacy & Security.
- Scroll to the bottom and tap Developer Mode.
- Turn the switch on (it is under Security). An alert warns that Developer Mode reduces the security of your device. Tap Restart.
- After the restart, another alert asks you to confirm. Apple’s steps for iPhone: swipe up, tap Enable, and enter your device passcode.
- If a Trust dialog appears next, tap it and enter your passcode again.
The app should now open. If the Developer Mode option is missing, install the developer-signed app first, then check again.
With a free Apple ID, you may also need to trust your own developer account once: go to Settings > General > VPN & Device Management, tap your Apple ID under Developer App, and tap Trust. Our Untrusted Developer guide covers that screen.
How to Turn Developer Mode Off
Apple’s steps: turn off the Developer Mode switch in Settings > Privacy & Security and restart the device. Apple notes that apps from Xcode will not run on the device again until Developer Mode is back on, and the same goes for apps signed by SideStore, AltStore or Sideloadly. Scarlet and apps installed through it are not affected.
Is Developer Mode Safe?
Developer Mode lowers one of iOS’s protections: it allows apps signed for development to run. That is fine for apps you chose to install yourself, but it is a reason not to leave it on without a need. Practical advice:
- Only install development-signed apps from sources you trust, and check IPA files before installing them.
- If you stop using AltStore or Sideloadly, turn Developer Mode off again in the same place. Apps signed with a development certificate will not open while it is off.
- Developer Mode is not a jailbreak and does not modify iOS; it is a standard Apple setting.
Developer Mode and the 7-Day Limit
Developer Mode only allows development-signed apps to run. It does not change how long their signature lasts. With a free Apple ID, apps signed by AltStore or Sideloadly still expire after 7 days and you can have at most 3 active at once; a paid developer account extends signatures to a year. If an app already stopped opening after a week, see how to refresh an app that expired after 7 days, and for the 3-app error see how to handle the free Apple ID app limit. Our comparison of AltStore vs Scarlet iOS vs Sideloadly covers these trade-offs, and how to sideload apps on iOS 26 and iOS 27 without a jailbreak walks through each method.
Quick Answers
Does Scarlet iOS need Developer Mode?
No. Scarlet uses enterprise-style signing, which needs the one-time profile trust step instead.
Do AltStore and Sideloadly need Developer Mode?
Yes, on iOS 16 and later, when apps are signed with your Apple ID.
Why can’t I find Developer Mode in Settings?
It only exists on iOS 16 and later. Apple says it appears once the iPhone has started pairing with a Mac or was paired before; it also tends to appear after a developer-signed app is installed.
Does turning off Developer Mode delete my apps?
No, but development-signed apps will not open until you turn it back on.
Is Developer Mode the same as trusting a profile?
No. Developer Mode is one switch for all development-signed apps. Trusting a developer in VPN & Device Management is a separate step per developer or certificate, and it is the only step Scarlet needs.
Does Developer Mode matter on iOS 27?
Apple’s steps are the same on current versions. Scarlet is confirmed on iOS 14 through iOS 26; iOS 27 support is reported by third parties but not officially confirmed.