Mods in single- and multi-player

Question

I have a question about mods for Minecraft.

I fumbled on the internet recently and I liked a few of them and I would like to play with them a little bit, but there is one thing that bothers me. The person with whom I play multiplayer via Hamachi wanted to stay with the regular version and did not upload anything.

What would happen if I have uploaded myself a mod that changes something in the game, and my friend does not? I would like to play in our shared world as usual (without mods) but when I create a new world for the single player I want the mods to work.

Is this possible?

Answer 1

Get and use MagicLauncher instead of the vanilla Minecraft launcher, and use its "profile" manager to set up one profile with mods for single-player and another profile without mods for multiplayer.

Because it loads mods dynamically, you don't have to alter the minecraft.jar, leaving you a perfectly-vanilla game for multiplayer. In your single-player profile's setup just add the mods to the lists of internal and external mods, and the launcher will add them to Minecraft only when you start the game with the single-player profile. When you want to play online, quit and restart to login with the vanilla, multiplayer profile.

Answer 2

There are very few mods that will work properly with out the server supporting them as well. Some of these you can get away with if you simply avoid what they provide but in general if the server you play on does not use the mods then you should likely avoid using them as well.

A mod that disables itself when in multiplayer is Somnia. A mod that you can just avoid using would be the book shelves (simply do not make them and it should be ok).

Hope this helps.

Answer 3

If you use the Technic/Tekkit pack, it comes with its own separate launcher that uses a separate save directory. It won't interfere with your vanilla Minecraft install or worlds.

For other mods, see this question: How do I keep two different versions of Minecraft installed?