Networked Play In Editor

Testing gameplay with clients and servers


Play In Editor supports multiple worlds, so that you can test networked play. The editor spawns multiple worlds within the already loaded instance of UE4, which results in fast iteration time and allows you to debug Blueprints for each world.

Setting up Networked Testing

In the Play In dropdown menu in the Level Editor Toolbar or Blueprint Editor Toolbar, you can set how many client worlds to create when you begin a Play In Editor session. In addition, you can specify whether or not to run a dedicated server.


The Number of Clients field allows you to specify the total number of players you want to test. If this is set to 1, and the Run Dedicated Server checkbox is unchecked, your Play In Editor session will allow you to test standalone, non-networked gameplay.

The other basic networking option provided in the dropdown menu is the Run Dedicated Server checkbox. When this is checked, a "dedicated server" world is launched, although there is no display or local player for the dedicated server. Using the dedicated server means that none of your clients will be running as a listen server. The dedicated server allows you to check for dedicated server only bugs, such as code that relies on a local player. A simple test configuration for Blueprints that have functionality that relies on servers and clients is to have Number of Players set to 1, and Run Dedicated Server set to true. There is only one window to test play in, but it has the full functionality of a client connected to a dedicated server.

After setting these options, pick your preferred Play In Editor mode to begin testing gameplay. If you have more than one client world and select the Viewport display type for your Play In Editor session, one client world will be shown in the viewport, and all others will be shown in new windows. The example image below shows testing with 4 players and a dedicated server.

Click to see full-size image:

You can use Shift+Tab and Control+Tab to cycle the focus between your client windows.

Advanced Settings

The number of client worlds, as well as whether or not to use a dedicated server, can also be set in the Level Editor - Play In Settings window. Here, you can also specify any command line options to be sent to the preview session. You can also revert to the previous networked Play In Editor behavior by unchecking the Use Single Process checkbox.



Number of Players

The editor and listen server count as players, a dedicated server will not. Clients make up the remainder.

Server Game Options

Additional options that will be passed to the server as URL parameters, in the format ?bIsLanMatch=1?listen - any additional command line switches should be passed in the Command Line Arguments field below.

Run Dedicated Server

If checked, a separate dedicated server will be launched. Otherwise the first player will act as a listen server that all other players connect to.

Route 1st Gamepad to 2nd Client

When running multiple player windows in a single process, this option determines how the game pad input gets routed. If unchecked (default) then the 1st game pad is attached to the 1st window, 2nd to the 2nd window, and so on.

            If it is checked, the 1st game pad goes the 2nd window. The 1st window can then be controlled by keyboard/mouse, which is convenient if two people are testing on the same computer.

Use Single Process

Spawn multiple player windows in a single instance of [API:UE4] . This will load much faster, but has potential to have more issues.

Debugging Blueprints

When running under a multiple world scenario, there is now an additional dropdown menu in the Blueprint Editor to select the world to debug:


The world list will filter Actors in the Actor list. For example, with "All Worlds" selected, you will see Actors from every world in the other drop down list. By selecting one of the other worlds, you will only see Actors in that world instance.

This also affects break points. For example, setting the debug world to Client 1 will make it so that only breakpoints will trigger on Actors in Client 1's world.

You can see the client number for a preview window by looking at the window title. For example, in the networked play image above, one window is titled ShooterGame Game Preview Client 1 (64bit/PCD3D_SM5)).

When All Worlds is selected, any world can trigger break points. When those break points are triggered, the blueprint editor will display which world it is debugging:


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