25 Free Game Modding Tools & Frameworks

Popular .NET mod loaders for Unity games. BepInEx and MelonLoader let you inject plugins and patch assemblies.
Use for: Unity PC mods, harmony patching, and asset replacement.

Mod.io SDK and Unreal mod support for UGC and cross-game mod distribution.
Great for: Unreal titles that want curated mod stores and community content.

Free 2D level and tilemap editor with export to many engines. Widely used for modding and indie level design.
Perfect for: custom maps, .tmx/.tmj pipelines.

Embeddable Lua used by many games for mod scripting (e.g. World of Warcraft, Roblox legacy).
Use for: mod scripts, game logic without recompile.

Godot projects as mods: load add-on projects or export scenes and scripts for community content.
Great for: Godot games with UGC support.

Unity Asset Bundles and Addressables for loading mod assets at runtime without replacing game files.
Use for: official mod pipelines, DLC-style content.

Nexus Mods hosting and Vortex mod manager for installing and managing mods (free for users and modders).
Perfect for: PC mod distribution, version and load order.

Steam Workshop API for publishing and subscribing to mods from within Steam.
Great for: Steam games that want one-click subscribe and auto-updates.

Open-source reimplementation of the Morrowind engine with strong mod support and cross-platform.
Use for: Morrowind modding, total conversions.

RPG Maker engines accept custom scripts (Ruby/JS) and asset packs for mods and new games.
Perfect for: JRPG-style mods, community games.

REDkit is the official modding tool for The Witcher 3 (and related RED engine content).
Great for: Witcher 3 modders, quests and worlds.

Open source engines allow full source mods and forks; Godot, Urho3D, and others support add-ons and custom builds.
Use for: total control, engine-level modding.

Community wikis (e.g. Nexus Wiki, game-specific modding docs) for formats, tools, and best practices.
Perfect for: learning pipelines and reverse-engineering file formats.