Minecraft Forums

Distributing a modded jar file is not allowed by the EULA:

Any Mods you create for Minecraft: Java Edition from scratch belong to you (including pre-run Mods and in-memory Mods) and you can do whatever you want with them, as long as you don't sell them for money / try to make money from them and so long as you don’t distribute Modded Versions of the game. Remember that a Mod means something that is your original work and that does not contain a substantial part of our code or content. You only own what you created; you do not own our code or content.

https://www.minecraft.net/en-us/eula

The key words here are "does not contain a substantial part of our code or content", which would apply to a whole working jar file (or "modded version") but not a relatively small patch that must be combined with an unmodified jar to get a working modded copy (such a method of modding would fall under "pre-run mods", mods which were already applied to Mojang's files, as opposed to "in-memory mods", which is how mods that use a mod loader work, applied to the game after it has been loaded in memory). Obviously, what "substantial" means is up to speculation but I've never seen any such mods, other than clearly illegal cracked clients, get taken down (e.g. a thread questioning the legality of Et Futurum, a mod for 1.7.10 which backports many features from newer versions by copying and altering the sources to make them work with 1.7.10; said mod continues to be regularly updated to this day (obviously, this by itself doesn't mean anything but I've never seen any issues raised by anybody who had their mod taken down or received a DMCA).

MCP itself has its own terms on what you can do; the biggest one may be the one regarding releasing any source code, whether they just mean unmodified vanilla code or what you modified or only code that is 100% yours is unknown but I generally haven't made any of my sources public for this reason (I've seen plenty of other mods with source that is clearly copied from vanilla, if not the original class):

You are allowed to:
- Use MCP to decompile the Minecraft client and server jar files.
- Use the decompiled source code to create mods for Minecraft.
- Recompile modified versions of Minecraft.
- Reobfuscate the classes of your mod for Minecraft.

You are NOT allowed to:
- Use MCP to do anything that violated Mojangs terms of use for Minecraft.
- Release Minecraft versions or modifications that allow you to play without having bought Minecraft from Mojang.
- Release modified or unmodified versions of MCP anywhere.
- Use any of MCPs scripts, tools or data files without explicit written permission.
- Make money with anything based on MCP (excluding Minecraft mods created by using MCP).
- Use MCP to create clients that are used for griefing or exploiting server bugs.
- Release the decompiled source code of Minecraft in any way.

(I'll note that the part about "[Make money with] Minecraft mods created by using MCP" is wrong as the EULA, or at least the current one since this was written in 2013, clearly states that you can't make any money off of mods. Actually, the EULA from back then said the same thing as the current one).

As far as distributing such mods, I distribute my own by distributing the files that MCP places in the "reobf" folder after running the "reobfuscate.bat" file, which contains all the modified and new class files (if it contains any unmodified files then you likely did something like change the type of a field or method; I've deleted upwards of 200 vanilla class files to avoid this, as well as possible errors due to referencing the wrong classes, and keep the number of files/recompilation time down). I also distribute a json file which has been modified to change the version "id" and remove the download URL for the client jar (otherwise the launcher will overwrite the modified jar with a clean copy). Installation is pretty much the same as in the old days; make a copy of the 1.6.4 folder in .minecraft\versions, rename it and the jar inside, replace 1.6.4.json with the one I provide, open the jar with an archive tool, add the files in the "mod" folder of the download and delete META-INF:

Here is the download for my namesake mod, you can browse through it online without downloading anything:

https://www.dropbox.com/scl/fi/tssvedc0xhb6dk6anap41/TMCWv5.10.zip?rlkey=rf98ln8zcmn52kttvv7mb1umg&dl=0

I'll note that I try to avoid directly modifying vanilla classes as much as possible, which is why there are so many files with the name of something from vanilla (e.g. instead of simply modifying "BlockAnvil" "BlockAnvilTMCW" extends the original class to add a 4th damage state and fix issues with collision boxes and use custom falling sand code, and add custom mechanics unique to the mod). Other classes may completely replace the original because I modified pretty much the whole class, even classes I didn't replace/override are usually extensively modified, e.g. the "World" class, which has 75% of its original lines modified in some way, others, like "RenderBlocks", were turned into a "wrapper" that redirects to my own code so I don't need to change every reference to it (to say that TMCW is a very invasive mod is putting it lightly, a lot of core code has been completely rewritten, along with many of my own methods added to support new functionality. This leads to the biggest issue with such mods and why they are looked down upon, mod compatibility (Optifine is infamous in the modding community for this reason), though in my case I don't care since I'm the main audience of my mods and don't use any other mods, though I have people pressure me to add features like Too Many Items, mipmapping and even shaders (and from where? I've seen others want to integrate Optifine into their MCP mod / custom client but its creator has a strict copyright about distributing it, same for TMI even if the developer hasn't been active in years).