While some mods do not affect your saved games, others do, and if they no longer function, then you may not be able to continue to play that city. This should be noted on their workshop page. Some mods may require other mods in order to function properly. Some mods that make changes to the same parts of the game may conflict with one another. Mods can change gameplay and depending on what the mod does, could make achievements easier, therefore achievements are disabled when mods are active.

Modders can remove or alter their work without notice at any time. If you use mods, while many may be updated quickly, you may have to wait hours/days/weeks for them to be updated after a patch, during which time your city could be unplayable (starting a new city is an option). There are many mods available, and Colossal Order cannot be expected to ensure that they will all still work after a patch, though they often work with modders to help them know what is coming. Often when game patches are released, information on mod incompatibilities gets posted on the Cities Skylines Paradox forum by helpful fans. Many mods will be updated by their creator or others, while some may no longer be supported. Mods make changes to or add to the game code, and when the game is updated ( patched), some mods may stop working properly. Mods are executable code, and as such there is always some risk in running code that you do not know the contents of. There are many mods in the Steam Workshop that can be amazing to use, and this section is not meant to discourage their use, but there are some downsides which you should be aware of.

Unlock All - Progression milestones are always unlocked.

Unlimited Soil - Landscaping without limits.

Unlimited Oil and Ore - Oil and Ore are not reduced from terrain.

Hard Mode - More challenge for experienced players.

In the game's main menu, they are found in the Content Manager in the MODS section, where they may be turned on or off. There are a few 'built-in' mods that come with the game.

Unlimited money cities skylines mods