Quick answer: you pressed Build in Visual Studio or Rider while the Unreal Editor is open with Live Coding on. Unreal only lets one of them compile.
- Small change inside a function? Go back to the editor and press Ctrl+Alt+F11. Live Coding patches it in.
- Changed a header, added a UPROPERTY, UFUNCTION or new class? Close the editor, build in your IDE, then open the editor again.
- Prefer building from your IDE? Turn Live Coding off in Editor Preferences > General > Live Coding.
The error
Unable to build while Live Coding is active. Exit the editor and game, or press Ctrl+Alt+F11 if iterating on code in the editor or game
Visual Studio or Rider shows this when you build the Editor target while an editor with Live Coding is running.
What Live Coding can and can’t do
Live Coding recompiles your C++ while the editor stays open. It’s fast, but it has limits.
| Change | Live Coding | Close editor and build |
|---|---|---|
| Code inside an existing function | Yes | Also fine |
| New UPROPERTY or UFUNCTION | Not reliable | Yes |
| New class, struct or enum | No | Yes |
| Changed class members or a USTRUCT layout | Not reliable | Yes |
| Constructor default values | Only new objects get them | Yes |
| Build.cs, Target.cs or .uplugin changes | No | Yes |
When in doubt, close the editor and build. It’s slower, but nothing gets corrupted.
Step 1: Use Live Coding for small changes
- Save the file in your IDE (don’t build).
- In the editor, press Ctrl+Alt+F11.
- Wait for the Live Coding window to say it succeeded.
Step 2: Build from the IDE for bigger changes
- Close the Unreal Editor completely, including any standalone game you started from it.
- Build the Development Editor configuration in your IDE.
- Open the project again.
Don’t save Blueprints that use a class you’ve just changed with Live Coding. If something looks wrong after a Live Coding compile, close the editor without saving, build from the IDE, then reopen.
Step 3: Turn Live Coding off (optional)
If you always build from your IDE, open Edit > Editor Preferences > General > Live Coding and untick Enable Live Coding. Restart the editor. The IDE build then works while the editor is closed, as before.
Still blocked with the editor closed?
A crashed editor can leave the Live Coding console running in the background. Open Task Manager, end any LiveCodingConsole or UnrealEditor process, then build again.
FAQ
Is Live Coding the same as Hot Reload? No. Live Coding replaced Hot Reload in UE5 and is much safer, but it still can’t add new reflected types.
My Live Coding compile succeeded, but nothing changed. Check that the code actually runs again: a BeginPlay change only runs for actors spawned after the patch. Restart Play in Editor.
Can I build the game (not Editor) target with the editor open? Yes. The message only blocks the Editor target, because that’s the one Live Coding is patching.