Skip to main content

Modding Video Games

Alton, IL. A custom world space and story for Fallout 3 by Elijah Houck.

Alton, IL. A custom world space and story for Fallout 3 by Elijah Houck.

A lot of people don't realize that you can mod PC games to make them do things the developers didn't intend them to do. Consider this your short tour guide to the weird and wonderful world of modding.

Mod is short for modification and it can apply to pretty much anything. Some of you may be familiar with the term as it applies to customizing a computer chassis to make it look different (like a Borg ship, for example) or creating mod chips for (hacking) game consoles but this hub is specifically about modding video games for the PC. (At the present time, it is not possible to mod console games, though that may be changing in the near future.)

No More Room in Hell bridges the gap between a mod and a professional game.

No More Room in Hell bridges the gap between a mod and a professional game.

What Types of Mods are There?

There really isn't much of a limit to what you can do with a mod if you know what you're doing. Mods like Dear Esther, No More Room in Hell, and Nehrim demonstrate what is possible for a dedicated team of modders. Of course, some games are much easier to mod than others.

In a worst-case scenario, a modder has to reverse engineer the game code in a decompiler or disassembler to make any sort of alteration to a game. This sort of modification is usually a violation of the EULA and is generally illegal (so don't try it at home), but there are many forms of modding that are legal and even encouraged by publishers. Here are a few of the most common types of mods:

Texture Replacers and Skins

It's something of a standing joke in the mod community that the first mod that any game gets is a nude patch. These mods are often the easiest to make (though hard to make well, I hear :) ). If you think of a 3D model as a box, you can think of its texture as the wrapping paper applied to the outside of it. By changing the wrapping paper, you can make the box look different. This wrapping paper is known as a texture map or skin. Reskinned objects are a very common kind of mod, though depending on the community you're in, it might be called a texture replacer or retex instead. Texture replacers can make any in-game object look different, though it will still behave the same way: characters, buildings, guns, creatures, and landscapes are all frequently retextured by modders. Texture replacers are generally quite easy to do because all you need to do is extract the original textures from the game and change them in an image editing program like Photoshop or the Gimp.

Closely related to object retextures are menu and HUD (heads-up display) retextures. These can sometimes be problematic depending on the game because many games treat this information differently but many games do support this type of mod. These kinds of mods are referred to simply as 'new skins'.

Custom Models

More ambitious and tech-savvy modders may go the extra step and create entirely new models for a game, or modify the original models in some way. This requires the modder to extract the models (and usually the textures as well) and edit them in a 3D modeling package like 3D Studio Max, Maya, or Blender. 3D modeling packages are difficult to master, so there tend not to be as many model replacers or custom models as textures, though there are quite a few of these as well. Getting completely original models into a game can sometimes be difficult due to import limitations on file types: you may need to own the same modeling package that the developers used to create custom models for it.

Custom Animations

Even more difficult (and rare) are custom animations. Animation is a notoriously difficult skill to master (large game developers use motion capture technology to create animations for human actors and are experimenting with motion capture for facial animation as well) but is essential for creating certain types of mods. If you want your characters to be able to use some fancy new combat moves, or you want to create a completely custom creature, you're going to need some animation. Animators suffer from the same import limitations that modelers face, but are even more likely to run into technical barriers. Getting custom animations working in-game is generally one of the hardest tasks facing a modder.

Custom Music, Sound Effects, and Voices

I put these all under the same category because they generally face the same sorts of obstacles. In general, it is not much more difficult to swap out music files or sound effect files than textures. Custom music packs are a fairly popular type of mod, though they usually 'borrow' music from somewhere else. Completely custom musical scores are generally quite rare but are a real treat if you can find a good one. Voice replacers are relatively rare for a couple of reasons: for one, they sometimes face import limitations not encountered when swapping out sound or music files, and two, it is really hard to find good voice talent. Anyone who plays video games knows this already! Custom voice dialogue is usually the preserve of custom quests or missions or total conversions.

Check Out Some of the Amazing Games You Can Mod

God Mode and Game Overhauls

Another very popular type of mod is the 'god mode' mod, where the modder makes the player's character more or less invincible. After struggling to beat the game the first time, it can be fun for a lot of people to replay the game in god mod and smack the dickens out of opponents that once made their blood run cold.

At the other end of the spectrum are rebalancing mods that aim to improve the gameplay balance to make it more challenging or fun. Realism or simulation mods are very popular, such as 'one hit kill' type mods that make weapon damage very realistic, or 'survival' mods that force the player to eat, drink, and sleep to improve immersion. These kinds of games are often referred to as 'overhauls' as they seek to adjust the data for the entire game to bring it inline with the modder's vision of the ideal game. Mods that change player or enemy stats, or the stats associated with weapons and health kits require either a level editor with access to these values (many editors supply this) or access to the source code or a portion of the source code. Depending on the game, therefore, these mods can be very easy to make or very difficult. In Oblivion, changing the amount of damage that a weapon does is about the easiest type of mod you can make: just open the editor, find the right object, change the value, and save. In Half-life 2, making changes like this require at a minimum downloading and installing compilers and SDKs and editing and recompiling source code; in other words, a minimum of programming knowledge.

AI Overhauls

A more complicated type of overhaul is the AI overhaul. AI stands for artificial intelligence and it is one of the most difficult challenges facing game developers. AI modders try to fix things like 'psychic' enemies (who always seem to know where the player is even when they have no way of knowing), unintentional 'zombies' (who stand around and do nothing even when being attacked), 'blind' bots (who can't find their way around level geometry and get stuck running on the spot), etc.

Because it is so hard to do well, many modders attempt to improve the AI in a game through various sorts of scripting hacks. If they are particularly talented and knowledgeable and have access to the appropriate source code, they may try rewriting portions of the AI engine itself. AI overhauls are generally more difficult to create than game rebalancers and can easily become one of the most difficult types of mods to create successfully.

Custom Shaders

After AI, probably the next most difficult type of mod to make is a custom shader. Shaders refer to the way a scene is rendered by the GPU (graphics programming unit). Shaders can be used to simulate effects like God rays, motion blur, depth of view, realistic light and shadows, etc. Shaders can make even older games look very, very good (sometimes almost as good as current games) but are very resource-intensive and not everyone can use them without reducing their games to a slideshow. Creating custom shaders requires an understanding of shader programming so they tend to be less common than other types of mods, though almost every major game has at least one person working on custom shaders.

Silgrad Tower extends the world of Oblivion on a massive scale.

Silgrad Tower extends the world of Oblivion on a massive scale.

Elsweyr, the Deserts of Anequina is another provincial expansion mod with similar breathtaking vistas.

Elsweyr, the Deserts of Anequina is another provincial expansion mod with similar breathtaking vistas.

Custom Levels, Maps, Quests, Missions, and Total Conversions

These are a very popular type of mod and the type most often supported by the developers. Many games come with level or world editors that allow you to create new levels using the assets that come bundled with the game. (For custom assets, see the sections above.) The simplest type of mod in this category is the custom level, or map, which is really just a new game environment populated with opponents and a thin story that gives you a reason for exploring or escaping the environment. (Groups of custom levels are often released as 'map packs'.)

The next most difficult kind of mod is the custom quest or mission (depending on your genre; they are the same thing). These generally involve one or more custom levels plus new characters, possibly voiced dialogue, and a longer, more involved story line with stages that have to be completed. Most level editors give you some way to create quests either directly or through scripting.

The most complicated type of mod in this category is the total conversion. Total conversions are rare and demand an unusually high amount of dedication and teamwork. They are often started by new modders and quickly vanish into oblivion. Total conversions are generally only completed by experienced mod teams and are similar in scale and scope to the original game. True total conversions generally require completely custom music, art, and story lines along with a lot of new scripted gameplay features. A good total conversion includes something from pretty much every other category on this list.

Mod Tools and Unofficial Patches

As amazing as all of these mods can be, nothing is more amazing than the dedication and ingenuity that modders bring to the creation of custom mod tools and unofficial game patches. Programmers write import and export scripts for custom assets, mod loaders and managers, model and texture viewers, and a host of other tools to assist the modder in his endeavors. Many of these are highly sophisticated pieces of software in their own right and are frequently used to fix bugs in the original game that the developers are no longer able or willing to fix: crashes, poor performance, and graphical glitches are all frequent targets for talented programmers. Some bugs may be fixed in the form of a mod: buggy quests may have their scripts fixed, poorly designed or optimized models or textures may be replaced, and missing content may be restored. These types of mods are typically a communal effort and 'must have' mods for serious mod users.

Is it Illegal to Mod a Game?

Well, it depends. Modding is a legal grey area and there aren't always hard and fast rules when it comes to mods but there are a few general rules that you should adhere to:

  1. In general, the EULA decides what is legal or not legal. If the EULA says you can't do something, you can't. Most EULAs will tell you that it is illegal to decompile a game, for example. In this case, if the publisher hasn't created any mod tools or made assets available to the end-user, it is illegal to reverse engineer the game to mod it. Just because you're not allowed to decompile a game doesn't mean you're not allowed to mod it, however; you just have to read the license to see what's permissible.
  2. It is illegal to redistribute a game or portions of a game. In other words, you can't include any of the original assets from a game with your mod. That's copyright infringement. In order to use a mod, the player has to own the original game. Your mod can only substitute custom (original, made by you) or modified versions of an asset, not the original asset. It is okay, for example, to distribute a new 'skin' (texture on the outside of a model) but not the original model that is being re-skinned. The user has to own a legal copy of that model, which they received when they purchased the game.
  3. Generally, it is illegal to sell mods. Even if the publisher creates mod tools and encourages you to mod their games, it is pretty much universally illegal to sell your mods, so don't even try. Most publishers are very strict about this. Some publishers, Epic, for example, allows you to buy a license to sell games made using their engine, however, and the rates are very reasonable. If you are interested in creating and selling games using an engine I recommend you look into UDK, Unity, and CryENGINE 3 for starters.
  4. It is illegal to mod online multiplayer games. Mods that give you an unfair advantage in a competitive online game are pretty much universally illegal. Depending on the game, you may be able to make mods of single-player elements, however.
  5. It is generally illegal to create mods using another person's intellectual property (IP). This is another type of copyright infringement. Basically, it is generally illegal to create a Star Wars or Batman mod without permission from the owner of the IP. This has to do with branding issues: the owners of these properties don't want people receiving undesireable impressions of their properties. Fan fiction suffers from the same sort of restrictions. To be honest, a lot of people get away with mods of this sort, at least for a while, so you will see them all over the place. Copyright holders generally won't bother interfering with mod makers until the mod becomes very popular or the mod depicts the property in an unflattering light. If you want to pursue this sort of thing, just remember that the owners have every right to issue you a cease & desist.
  6. It is also illegal to create a mod that recreates another game, even an earlier game in a series. This falls under copyright infringement as well. These sorts of mods are also popular. Some publishers don't mind if you try to recreate an earlier game in their series with a newer engine but others take it very seriously. When in doubt, ask at the mod forums to see how a company will respond to this kind of mod.
Scroll to Continue

You can find a great, short discussion on the legality of mods by Mark Methenitis here:

A great resource for questions about copyright, reverse engineering and related topics can be found at

Books About Modding

Where Can I Find Mods or Learn How to Make Them?

Most games that support modding have their own online modding communities, usually centered around one or more forums, a download depository, and a central wiki. To find these communities, just Google the name of your game and add 'modding', and 'download', 'forum' or 'wiki' and see what comes up. You might have to dig a few pages depending on the game, but you'll likely find something of interest. You might also be able to find it through the 'community' link at the game's official web site. Publishers are often happy to connect fans with their favorite products.

One other great resource is the ModDB (mod data base). If there are mods for a game, you can pretty much bet that at least some of them are here. Most games have their own mod-distribution sites as well, however, so it pays to look around. For example, the Nexus network is the number one place to find mods for Bethesda games (Oblivion, Fallout 3, and Fallout: New Vegas, though they do other games as well) and there are literally tens of thousands of mods there.

(Shameless plug: I also run a web site called truancyfactory which is dedicated to modding and game design, mostly for Oblivion and Fallout 3 mods. Feel free to drop by and check it out.)


AmazingDamien on October 02, 2014:

I would like to mod Assassin's Creed games. Are these games even moddable? If they are, where can I find sites which could help me?

panda on September 25, 2014:

Can you reverse a mod ? If so how?

Nichlas on February 16, 2013:

Hello.. i am looking for someone who can help me making a mod for morrowind please contact me on

j-u-i-c-e (author) from Waterloo, On on November 21, 2012:

@furrykef: IANAL but I know of modders who have received cease and desist orders and been banned from publisher forums for trying to charge for their original additions to the game. Example: a modder who tried to charge for the original voice files included as an optional download with their mod. I'm pretty sure that any mod created using an official mod tool is a derivative work owned by the publisher according to their EULA. You might be able to fight some of these things in court but I doubt it would be worth your time/money.

Some things I could see getting away with: selling custom textures/models wholly created by yourself without using any game assets that are also NOT based on IP owned by the publisher. Example: I could sell a model of a car created using Blender and Gimp that happens to work in a game, but I couldn't sell a model of Batman because that character is a property owned by a publisher even if I did all the work myself. To have any chance at all you'd have to not only not use any assets or code, but also not use any IP. If there's even a hint that your infringing you'll get notice whether its defensible or not. Big companies hire lawyers to protect their assets/brand and they have deeper pockets than most modders. Plenty of mods get shut down for copyright infringement even though they're not charging a dime. (Example: Middle Earth for Skyrim/Oblivion.)

On the positive side, they do allow you to take donations for your work on places like Steam Workshop and Nexus, which is a huge step forward. That can get tricky too, though, since you can't 'withhold' mods or portions of mods in exchange for donations: that's the same as selling your work. If you're interested in making money off modding, your best bets are to sell 3d/texture art freelance or make kickass mods and ask for donations.

furrykef on November 21, 2012:

Are you sure about the illegality of selling mods? If a mod includes no code or assets from the original game in its files, I have a hard time seeing how it constitutes a derived (and therefore infringing) work, even if it integrates with the game's existing assets.

Are there any legal precedents on this issue?

j-u-i-c-e (author) from Waterloo, On on November 11, 2011:

Yeah, whether or not you can get away with a mod that 'borrows' a licensed product depends largely on the owner of the license. I've seen a few mods shut down over the years, but it's pretty hard to predict who will and when. Thanks for the reply.

kschang from San Francisco, CA, USA on November 10, 2011:

Nice guide.

Situation is even stickier if the developer had gone out of business, or was absorbed into labyrinth of corporate takeovers and neglected. Take Falcon 4 (the flight sim). MicroProse was absorbed into Hasbro, which was absorbed into Atari, which was absorbed into... whatever. Hackers went ahead and hacked the original binaries to improve the flight model and fix bugs. Then somehow mysteriously part of the source code got leaked onto the net, so REAL mods started to appear. Eventually an official version called Falcon 4: Allied Forces, reappeared briefly on the market, only to die again.

In many cases, the original copyright holder don't really care about the mod community. It's sort of "benign neglect". I think THQ had this attitude with Titan Quest, as the community patch exists but the developer, Iron Lore, is long gone.

As for Star Wars mods... I believe someone made a Darth Vader mod for one of the Star Wars Jedi games and it was yanked just before release due to pressure from LucasFilm.

So yes, there are stickier situations where one may get away with something. :) Don't cite internet examples as if it somehow disproves the advice given here. It just means the author wasn't slapped down yet. :D

Related Articles