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I'm wondering if I could play Minecraft with my friend. A modded Minecraft, only myself with mods and him without mods. Is it possible?

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No, you can only play multiplayer if you have the same version of Minecraft and the same version of mods.

It is however fairly simple to install something like Feed the Beast and have multiple copies of Minecraft installed at the same time, this way your friend can have mods to play multiplayer and when he's playing alone he can play vanilla Minecraft without having problems with his save files.

As @dlras2 mentioned, it can work if you only have mods that are client side, like mini maps. Basically anything that changes crafting or adds new blocks/items will not work without having the other player also having that mod (because all that is sent is "Hey, make this item" and the unmodded client will then go "I HAVE NO IDEA WHAT TO DO AND I AM PANICKING" and then probably crash)

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  • so we can only play when he have my mods ?
    – Asking12345678910
    Commented Jan 29, 2014 at 12:17
  • Jup, you need the exact same modset and configurations to play together. There are several options to have two installations of Minecraft on the same computer so that is a possible solution.
    – Elva
    Commented Jan 29, 2014 at 12:20
  • so thats answered ..
    – Asking12345678910
    Commented Jan 29, 2014 at 12:24
  • @Asking12345678910 if Kevin answered your question you should mark it as accepted by clicking the checkmark
    – Ender
    Commented Jan 29, 2014 at 14:32
  • Configuration doesn't matter - any modern mod loader will ensure that server-relevant config options are loaded from the server. As an aside, there's also some purely server-side mods that only add server-relevant content, such as crafting recipes. Nowadays these tend to be datapacks. However, as soon as it adds a new block or item or similar, it must exist client-side AND server-side.
    – Egor Hans
    Commented Mar 12, 2021 at 7:40
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It depends on the mods- Some mods are client-side only, and can be used without others needing them. An example of this would be minimap mods such as Zan's or Rei's, UI mods such as NEI/TMI, or shader mods. These mods don't add any new blocks or anything that your friend will be able to see- They simply change things on your client.

Generally, if a mod adds new blocks or entities (such as tools or monsters) then it will only work if both you and your friend have it installed. Other than that, a lot of mods will still work without your friend needing to install them too.

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    It might actually also depend on who hosts the game, no? I didn't test it, but I wouldn't be too surprised if an unmodded server would allow a modded client to connect and either ignore or kick them on an attempt at doing anything mod-related such as placing/crafting a mod-only item
    – Zommuter
    Commented Jan 29, 2014 at 17:07
  • @Zommuter That's correct, a modded client will be able to connect to and unmodded server, but not vice-versa. If the friend who is running vanilla hosts the server, then you could even connect with a massive modpack such as FTB (providing they both use the same version of minecraft)
    – Viprus
    Commented Jan 29, 2014 at 17:18
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    I know that a long time ago, there was a "broken" block that could be placed or come from map corruption that would freeze the game if it attempted to render it. It's possible something similar could happen in this situation.
    – Rob
    Commented Jan 29, 2014 at 17:19
  • @Rob More often than not, if the server doesn't know about the block, the player won't be able to craft, obtain, have or place the item. There are still some times when this will happen, but mostly from someone using an older version of the mod than is installed on the server.
    – Viprus
    Commented Jan 29, 2014 at 17:22
  • Also, some mods are server-side only (although most are in the form of "plugins", there are server-side mods that are not plugins)
    – AJMansfield
    Commented Jan 29, 2014 at 17:32
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It depends on whether they are client or server side mods. Something like NEI ( Not enough items ) or a minimap is a client side mod. These need to be installed only on the client. They are things that add UI (User Interface) Elements.

Anything that adds items or mobs is a server side mod. These need to be installed on both the server and the client.

So the short answer is maybe. If you do not know which they are, please ask. Hope this helps.

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It depends on what type of mod you are talking about, and whether you're are talking about LAN or actual servers.

If you're talking about LAN, then any mods that do not physically add anything into the game, such as TooManyItems, a minimap mod, or the shader mod, you should not encounter any problems. But if it's a mod that adds new items, like RedPower, or BuildCraft, then you will start to encounter problems with LAN.

If you're talking about an actual server, then any mods that do not add anything into the game, like I said above, ShaderMod, TooManyItems, and others, you will not encounter any problems. Yet, if they're mods that add items and blocks into the game, like BuildCraft or RedPower, as long as your minecraft versions are the same you should not encounter any errors when trying to connect, yet, if you attempt to get one of the items in the mod out of a Creative inventory, or another inventory, you will be kicked from the server.

If you're talking about putting mods on the server, all players will have to have that mod client-side to connect.

Long story short, If you're installing a client-side mod that doesn't add any new blocks, items, or entities, you'll be fine, If you get a mod that does add items, blocks, or entities, you will start to encounter some problems with LAN but you won't see as many on an acctual server. If you are installing a server mod, all players will have to have that mod client-side to be able to connect.

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Here's an answer from a more technical standpoint with examples:

A minimap plugin might work fine just on the client, without a piece on the server. This would be a minimap that works fine without a "server half".

Similarly, a plugin that shows you how many hearts of HP probably won't need to be on the server, because the normal client already knows all that's needed for it to work.

Some plugins, such as RedPower2, or AE set a "client must have" flag (in forge). This means that if the server has the mod running, the client must have it to play on the server. If the client didn't have it, the client would probably crash because there are blocks it doesn't understand. (slight over-simplification) On the other hand, if a client has AE installed, it can still connect to a "normal" server, because the plugin on the client is smart enough to "turn itself off" if the server doesn't have AE. In theory you could also have the server turn off AE if an incompatible client connected, but this would be silly, since it means that anyone could disable that mod for everyone just by connecting with a "bad" client.

Some plugins only run on the server, and the client doesn't care. These are usually plugins dealing with server permissions, message of the day, and plugins that do things when you make special signs.

A few plugins will cause your client to crash if the plugin is only on the client. These are plugins that fundamentally change Minecraft so much that the server can't even talk to the client, or because the plugin changes vanilla blocks.

Usually:

*) If a plugin is for server admin, the client doesn't need it.

*) If a plugin adds blocks, modded clients can connect to a vanilla server, but vanilla clients can NOT connect to a modded server.

*) If the plugin is a small "player helper" such as a map, it will often work, no matter who has it.

*) Those last three points are guidelines, and not solid rules.

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