~~META:title=about tweaks~~
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What are 'Tweaks'?
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A **Tweak** is a special type of [[mod]] which is able to make changes to the game environment before and during the game load. This type of mod is typically used to make very low-level changes to the game code either because implementing the mod via a [[ModSystem]] would be cumbersome/impossible, because using a [[ModSystem]] is not desired, or because the mod is a [[ModSystem]] itself.

A **Tweak** can do several things that a regular mod cannot do:

* Alter or add to the **command-line arguments** which launched the game
* Specify an alternative **main class** for the game
* Make changes to the **game environment** before the game is launched (such as injecting extra ''.jar'' files into the game or altering system properties)
* Inject into the [[ClassLoader]] and provide [[transformers|Class Transformers]].

It is the last capability which makes **Tweakers** so powerful, since hooking into the game's [[ClassLoader]] allows almost unlimited control over the game's internal code.

Differences to "Core Mods"
==========================

**Forge ModLoader (FML)** has a capability for a mod to elect to become a *"core mod"* which sounds very similar to the features just described for Tweakers above, and this is no coincidence. This is because **FML** is a **Tweak** itself and chooses to delegate its power to "core mods" which require it, any **Tweak** can do this and LiteLoader does so as well, although it doesn't make a distinction between "core mods" and "regular mods" and simply lets any mod supply [[transformers|Class Transformers]] if it wants to.

In a nutshell, a "core mod" accepts delegated power from a **Tweaker** without becoming a **Tweak** itself, this makes it dependent on the first **Tweaker** and not on the Tweak System directly.

How do they work?
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Whilst it is incredibly powerful, the Tweak System itself is actually incredibly simple. It leverages a library called [LaunchWrapper](https://github.com/Mojang/LegacyLauncher) originally written by [[people:cpw]] for Mojang in order to allow them to run old versions of Minecraft inside the new launcher. To use **Tweak**s, **LaunchWrapper** is simply added to the game environment and the game's **main class** is replaced with **LaunchWrapper's main class**. Tweak classes can then simply be specified on the command line using ''--tweakClass'' arguments.

Multiple Tweaks and CascadedTweakers
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Since the original aim of *LaunchWrapper* was to allow old versions of the game to be run in the new launcher, there was no provision made to allow more than one **Tweak** to be specified at a time. In version 1.7 of *LaunchWrapper*, [[people:cpw]] added the ability to specify multiple tweaks, but prior to that a contract of '*cascading*' tweakers was agreed between [[people:cpw]] and [[people:mumfrey|myself]] to allow whichever tweaker was loaded first to load the other.

This is why in newer versions of Minecraft you can simply specify multiple ''--tweakClass'' arguments but before that it was necessary to specify the first tweak using ''--tweakClass'' and additional tweaks using ''--cascadedTweaks''