Many mods are not publicly released to the gaming community by their creators. Some are very limited and just include some gameplay changes or even a different loading screen, while others are total conversions and can modify content and gameplay extensively. A few mods become very popular and convert themselves into distinct games, with the rights getting bought and turning into an official modification.
Technical and social skills are needed to create a mod.
A group of mod developers may join together to form a "mod team".
Doom (1993) was the first game to have a large modding community. In exchange for the technical foundation to mod, id Software insisted that mods should only work with the retail version of the game (not the demo), which was respected by the modders and boosted Doom's sales. Another factor in the popularity of modding Doom was the increasing popularity of the Internet, which allowed modding communities to form. Mods for Quake (1996) such as "Capture the Flag" and "Team Fortress" became standard features in later games in the shooter genre. While first-person shooters are popular games to mod, the virtual pet genre with games such as Petz (1995) and Creatures (1996) fostered younger modders, particularly girls.
Mod-making tools are a variety of construction sets for creating mods for a game. Early commercial mod-making tools were the Boulder Dash Construction Kit (1986) and The Bard's Tale Construction Set (1991), which allowed users to create game designs in those series. Much more successful among early mod-making tools was the 1992 Forgotten Realms: Unlimited Adventures from Strategic Simulations, Inc., which allowed users to construct games based on the game world that was launched with the Pool of Radiance game.
By the mid 1990s, modding tools were commonly offered with PC games, and by the early 2000s, a game that launched with no modding tools was considered more worthy of note in a review than one that did. Maxis released the modding tools for The Sims (2000) before the game itself, resulting in a suite of fan-created mods being available at launch. The advertising campaign for Neverwinter Nights (2002) focused on the included Aurora toolset. The provision of tools is still seen as the most practical way that a company can signal to fans that its game is open for modding. Fans may also use and create open-source software tools for modding games.
There are also free content delivery tools available that make playing mods easier. They help manage downloads, updates, and mod installation in order to allow people who are less technically literate to play. Steam for Half-Life 2 mods is an example.
Game support for modifications
The potential for end-user change in game varies greatly, though it can have little correlation on the number and quality of mods made for a game.
In general the most modification-friendly games will define gameplay variables in text or other non proprietary format files (for instance in the Civilization series one could alter the movement rate along roads and many other factors ), and have graphics of a standard format such as bitmaps. Publishers can also determine mod-friendliness in the way important source files are available, such as Doom having its art assets separate from the main program, which allowed them to be shared and modified.
Games have varying support from their publishers for modifications, but often require expensive professional software to make. One such example is Homeworld 2, which requires the program Maya to build new in-game objects. However, there are free versions of Maya and other advanced modeling software available. There are also free and even open-source modeling programs (such as Blender) that can be used as well.
For advanced mods such as Desert Combat that are total conversions, complicated modeling and texturing software is required to make original content. Advanced mods can rival the complexity and work of making the original game content (short of the engine itself), rendering the differences in ease of modding small in comparison to the total amount of work required. Having an engine that is for example easy to import models to, is of little help when doing research, modeling, and making a photorealistic texture for a game item. As a result, other game characteristics such as its popularity and capabilities have a dominating effect on the number of mods created for the game by users.
A game that allows modding is said to be "moddable". The Elder Scrolls V: Skyrim as well as its predecessors, The Elder Scrolls III: Morrowind and The Elder Scrolls IV: Oblivion, are examples of highly moddable games, with an official editor available for download from the developer. Daggerfall was much less moddable, but some people released their own modifications nevertheless. Some modifications such as Gunslingers Academy have deliberately made the game more moddable by adding in scripting support or externalizing underlying code. Supreme Commander set out to be the 'most customisable game ever' and as such included a mod manager which allowed for modular modding, having several mods on at once.
The games industry is currently facing the question of how much it should embrace the players' contribution in creating new material for the game or mod-communities as part of their structure within the game. Some software companies openly accept and even encourage such communities. Others though have chosen to enclose their games in heavily policed copyright or Intellectual Property regimes(IPR) and close down sites that they see as infringing their ownership of a game.
For cross-platform games, mods written for the Windows version have not always been compatible with the Mac OS X and/or Linux ports of the game. In large part, this is due to the publisher's concern with prioritizing the porting of the primary game itself, when allocating resources for fixing the porting of mod-specific functions may not be cost-effective for the smaller market share of alternate platforms. For example, Battlefield 1942, ported by Aspyr for Mac OS X, had file access issues specific to mods until the 1.61D patch. Unreal Tournament 2004 does not have a working community mods menu for the Mac OS X version and, until the 3369 patch, had graphics incompatibilities with several mods such as Red Orchestra and Metaball.
Also, mods compiled into platform-specific libraries, such as those of Doom 3, are often only built for the Windows platform, leading to a lack of cross-platform compatibility even when the underlying game is highly portable. In the same line of reasoning, mod development tools are often available only on the Windows platform. id Software's Doom 3 Radiant tool and Epic Games' UnrealEd are examples of this.
Mod teams that lack either the resources or know-how to develop their mods for alternate platforms sometimes outsource their code and art assets to individuals or groups who are able to port the mod.
The mod specialist site for Macs, Macologist, has created GUI launchers and installers for many UT2004 mods, as well as solving cross-platform conversion issues for mods for other games.
Unforeseen consequences or benefits of modding
In January 2005, it was reported that in The Sims 2 (2004) modifications that changed item and game behavior were unexpectedly being transferred to other players through the official website's exchange feature, leading to changed game behavior without advance warning.
After the Hot Coffee mod incident, there were calls from the industry to better control modders. There is concern about mods which show nudity, and Bestheda does not allow mods with nudity to be uploaded on its website. Nexus allows for mods which allow nudity if breasts are not visible in the preview image. One of the most popular mods of this type is Caliente’s Beautiful Bodies Edition, which allows for body modification in Skyrim and Fallout 4, and has been downloaded at least 8.2 million times.
In 2015, members from the Grand Theft Auto fan site GTAForums reported instances of malware being circulated through modifications written using the .NET Framework for Grand Theft Auto V. Two of the modifications in question, namely "Angry Planes" and "No Clip", came with code for loading a remote access tool, and a keylogger for stealing Facebook and Steam account credentials. The modifications in question have since been taken out of circulation, with affected players being advised to change their social media account passwords and disinfect their computers.
Motivations of modders
The Internet provides an inexpensive medium to promote and distribute user created content like mods, an aspect commonly known as Web 2.0. Video game modding was described as remixing of games and can be therefore seen as part of the remix culture as described by Lawrence Lessig, or as a successor to the playful hacker culture which produced the first video games.
Mods can be both useful to players and a means of self-expression. Three motivations have been identified by Olli for fans to create mods: to patch the game, to express themselves, and to get a foot in the door of the video game industry. However, it is very rare for even popular modders to make this leap to the professional video game industry. Poor suggests becoming a professional is not a major motivation of modders, noting that they tend to have a strong sense of community, and that older modders, who may already have established careers, are less motivated by the possibility of becoming professional than younger modders.