When Paradox Interactive started to work on their city builder the team decided to integrate mod-support and Steam Workshop from the beginning on: the best choice they could take as their experience shows.

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When we started working on »Cities: Skylines«, we knew from the start that modding would have to be an integral part of the product. »Cities: Skylines« was the first game from Paradox Interactive where we went up against an established AAA-title in a non-niche genre, and we simply lacked the resources to compete in terms of assets and production value.

This made modding a target of one of the game’s most obvious flaws, and we implemented it early as one of the demands of the product. We also decided that in order to keep costs low and to let Colossal Order, the studio that developed »Cities: Skylines«, focus on doing what they do best so that we would build the whole game from start around Steam Workshop.

Integrating modding into the game would always be a bit of a challenge, Unity as an engine has never been the most mod-friendly, but Colossal proposed great solutions on how to run the code to make it more accessible. We also decided to design native tools for importing and exporting 3D objects into the game to be used in the asset editor for easy creating and sharing of assets.

While we had hoped that the modding tools of »Cities: Skylines« would be popular, nothing prepared us for the reception they got. Just a few days after release, we had tens of thousands of pieces of content and mods on Steam Workshop, and it soon became clear to us that the majority of players used this option to enhance the gameplay.

The rest of this article will ask why it was so successful and what lessons can be learned from our experiences.

Modding as philosophy

In many ways, modding in game design boils down to a philosophy; do you sell a finished set experience to the player that you know they will enjoy as you intended or do you create the so often spoken about sandbox where players shape and create their own experience with a set of tools, rules and possibilities?

The AAA industry has always been dominated by the former thinking, which is natural. They have enormous budgets but also need to sell enormous amounts of copies which always will be easier the less you demand of the player (or at least that’s the way it might seem). Paradox Interactive on the other hand grew up way out on the other side of the scale, creating vast and rich sandboxes on tight budgets. Our experiments with post-release patching and DLC (long before either was a norm) often rose out of necessity rather than choice but it proved the strength of digitally distributed content.

Already with the original »Europa Universalis« the first game-changing mods started to arrive, and I remember playing them myself as a 16 year-old. It was the start of Paradox’s relationship with modding, and over the years several games have been released since based on mods made by the community.

When we started working on »Cities: Skylines« it was obvious that not only did we want to continue this tradition but we also wanted to push it further than before. Instead of seeing modding as something added later to the game as a possibility for a few dedicated users, we wanted to integrate it into the heart of the game.

Content vs. Systems

One of the main reasons behind the choice to prioritize modding tools and the modding API was the choice between content and systems. The core team at Colossal Order started off with only 9 people, and despite growing to 13 during the project and the use of 3rd party graphic studios, there were always hard choices to be made. Our earlier experience with games like »Europa Universalis« and »Cities in Motion 2« told us that even a fairly small player base will create quite an extensive amount of mods and content if you use Steam Workshop. In the case of »Cities in Motion 2«, a 2013 mass transit simulator from Colossal Order and a game that in many ways exemplifies niche, has at the time of this writing around 1,000 pieces of content on Steam Workshop.

That smaller teams, especially Indies, should focus on systems ahead of content is of course nothing new, but it is maybe not commonly understood how much a file sharing platform such as Steam Workshop can help a game to overcome limitations in content. Games such as city builders are based on the people’s love to create, and if you give them good tools and good possibilities to share even a fairly small user base will quickly start creating assets. For a game with a large active community, the sky is the limit, often generating full new game experiences.

This part of modding can often seem problematic to the developer; the more you unlock for the user the harder it will be for the developer to have control of the experience. The developer will often want to focus more resources on bringing their own ideas into the game than facilitating the same opportunities for the players. This is only natural, most developers want to make game experiences, and not feel like a glorified engine maker and want to maintain control of the creative vision of the game.

However, there can be a great and unique experience in working close with a community and developing a game together, blurring the line between player and developer, creator and consumer. The role of the publisher here should often be to try and help the developer to feel secure in focusing resources on the modding tools rather than adding to core game experience.

Steam Workshop in the game

One of the most important decisions regarding the actual implementation we made regarding »Cities: Skylines« was to design our modding tools and Steam integration from start. Previous games made by Paradox Interactive had the Workshop added at the end of the project, almost as an afterthought. The games were designed to be full experiences in themselves and modding seen as a boon for the dedicated few that wanted them.

With »Cities: Skylines« we took another route. We designed all tools and implementation from day one and decided to use a design that would have the mods integrated in the core game loop, even using the mod systems for different game modes and options. We also decided not to use an in-game store but instead integrate Steam to make all the systems as close to each other as possible.

Integrating Steam Workshop into the design was fairly straightforward once the decision was made. As mentioned earlier, Unity has never been the most mod-friendly engine, but the folks over at Colossal Order did an amazing job in opening up the engine, building great tools and taking a holistic view on modding in the game design.

One thing we did not fully take into account, and that will be discussed further down in the article, was how to work with continued development in an environment where most players use mods, something often not fully understood even by the studio. Truth be told, we are still working on solving the problem, but more on that later.

One thing that has proved more successful than we ever expected was how well the community on Steam Workshop has monitored itself. Despite having tens of thousands of mods that potentially could be harmful (»Cities: Skylines« allows for .dll-modding which can be used to create viruses and other forms of malware), no serious problems have aroused. The community quickly arranged for an approval method based on »Reddit«, and still today the amount of flagged content is in the low tens.

Another thing that worked a lot better than expected was the media pickup. Within weeks the mods for the games got more press than the game itself, continuing to gather pick up for the title and generating great buzz. PC Gamer still has a continuously updated article called »Best mods of Cities: Skylines« that keeps the game in players’ mind.

Modding post-release

One of the greatest challenges and maybe the only negative surprise of using Steam Workshop with extensive mod support has been with patching and updating the game as it is live. The most popular mods on »Cities: Skylines« have hundreds of thousands of subscribers, which means that if any of those are broken with a patch, severe player reactions can occur.

We are still working on finding a solution around most of the problems. As a game becomes more popular and the modded experience becomes as common as the vanilla experience, the idea of owning the game and the experience becomes blurred. Paradox’s line here has been clear, in the end we are the ones promising to deliver a good product to the player, because of that we also need to make sure that we can take final responsibility for said product. With tens of thousands of mods, there is no way for us to ever ensure that all of them work when a patch is deployed, therefore the most straightforward solution is to take responsibility for none of them. That doesn’t mean that we will not try to help modders in quickly patching their content, but the responsibility must lie with them.

In the last part of this article I would like to discuss the future of modding, both in »Cities: Skylines« in particular and gaming in general. But before I get into that, let me summarize the experiences with modding in »Cities: Skylines«:

»Cities: Skylines« has been Paradox Interactive’s greatest success to date, and while we had high hopes for the product we never expected what came. It cannot be understated how important modding was in making this happen. The game, however good, had some natural limitations due to the size of the team and Steam Workshop was a key factor in overcoming these short comings. I would recommend any publisher or developer to never hesitate in spending time and resources not only on making modding available, but to also try to develop tools and APIs to facilitate for the creators. Even fairly niche games will get an active community, and it will help your product; end of story.

The Future

So what is the future of modding? First of all, let us start with acknowledging that mods have for a long time defined PC gaming, maybe more than people have been willing to admit. Of the five most played games on Steam, three are based on mods. More and more of the PC’s bestselling games have added mod support and Steam Workshop, including titles like »Skyrim« and »GTA V«.

One of the great unresolved issues will be the monetization of mods. The classic way has been making full games out of successful mods, but these will only be for the full mods and not for the smaller content creators that make up the majority of the modders.

Valve has successfully found solutions, »Skyrim« had less luck with theirs. The exact nature of how this will end up remains to be seen, but I am personally convinced that more and more paid-for mods will become the norm. When hundreds of thousands, or even millions, of people use your content it is only fair that some sort revenue flows to you, the modder – the creator.

Jakob Munthe

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