Colossal Order Ltd

Colossal Order

Game Development Studio

Greetings everyone. We have a new mini-series of development diaries as we count down to the release of Cities: Skylines II. In this series, we take you behind the scenes of development sharing some of our processes and philosophy behind certain features as well as give you a sneak peek at our plans for the future. 

To start with, we’re going to talk about modding in Cities: Skylines II. While modding isn’t supported at release, we want to share what modding means to us and how we approach modding support, so you know what to expect. Modding in Cities: Skylines played an important part in making the game a success, so it was obvious to us that Cities: Skylines II also has to be moddable, and we can’t wait to see what the modders come up with this time around!


Our journey with modding started in a somewhat unexpected way with our first game, Cities in Motion. Back then, we hadn’t initially planned extensive modding support, but as the game used our own technology and was very accessible to players, a modding community grew surrounding the game. While not intentional we soon discovered how much modding can add to a game with players customizing their gameplay experience, creating and sharing content with each other.

We carried that lesson forward to Cities in Motion 2, though it wasn’t until Cities: Skylines that we really realized the full potential of supporting modding. As we were developing the game, we had one of our two programmers focus on creating tools to mod the game. When Cities: Skylines was released, we had a map editor, that let you create your own maps to build cities on, and an asset editor to import custom 3D models to the game. These, along with code mods, could then be shared on the Steam Workshop and downloaded by others. Through the years we expanded the capabilities of the asset editor to include more options, and as map themes and scenarios were added to the game, we included editors to make your very own.

Today, the Cities: Skylines Workshop has over 400,000 mods with everything from maps and themes to buildings and code mods changing the rules of the game. We were absolutely blown away by the creativity and dedication of our modding community, and throughout the game’s lifetime, we have continued to improve how we interact with the modders.

The built-in editor and easy sharing through the Steam Workshop brought more modding opportunities to Cities: Skylines than our previous games had.

When we started developing Cities: Skylines II, we knew we wanted the game to support modding as much as its predecessor did. In 2019, as part of our 10-year anniversary celebration, we invited a group of prominent modders to Tampere to help us determine how we can best support their modding efforts. We introduced them to the features Cities: Skylines II would come to include, as well as the level of detail and realism of its art style. We discussed their experiences modding Cities: Skylines and they provided great feedback on how we could support the community in Cities: Skylines II. As an example, our map creators expressed a wish to be able to create taller mountains and deeper valleys, and as you may have seen from our Maps & Themes development diary, this is possible in Cities: Skylines II. 

We support modding to celebrate the community and we want everyone to be able to take part in it. This is the reason why we focus on making sure that the modding tools are available on all possible platforms while respecting the limitations that individual platforms may have. To offer the same content for all the players we have chosen PDX Mods as our portal for sharing your amazing creations across all platforms.

Access the Editor and Paradox Mods directly from the main menu


We have always tried to offer as much support for the modders as possible and the modding beta was created for Cities: Skylines as a part of our efforts. The purpose of this was to ensure the modders could prepare updates for mods that might break with game updates. Having the opportunity to access the upcoming builds prior to release provided them time to familiarize themselves with the changes and work on and test updates to their mods.

As the Cities: Skylines Modding community grew, this group was expanded to include asset creators and its purpose expanded to provide direct feedback on the modding tools. The beta gave us the opportunity to get feedback on the road editor before it was released to the public and have direct conversations with our modders about what improvements to the game’s API would be useful to them. 

As the updates for Cities: Skylines have ended the modding beta shifted more towards testing and providing feedback on the modding tools in Cities: Skylines II. Currently, the modding beta is testing the Cities: Skylines II Editor, which we’ll dig into in the next development diary.

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