NoMissingMods

First, you should create a config describing the mods you don't want to install on the client.
Here is an example modlist.json for NotEnoughResources, NEI Addons and WAILA Plugins.

You have a few options to choose from, depending on your situation and convenience.

Manual rewriting (if there are few mods in the warning):
1. Open the MNMM folder with a modlist.json file inside in your client's config folder (.minecraft\config\MNMM\modlist.json). The folder will be created automatically when you join singleplayer or multiplayer.
2. Rewrite the mods from the “Mod rejections” warning to the modlist.json file in the format {"modid":"version","modid":"version"}.

Copying from the client* (if there are many mods or no access to the server):
1. Start the client with all mods and MiniNoMissingMods and enter the “/MNMM modlist” command (it's case-sensitive).
2. Take the MNMM folder with the modlist.json file inside, generated in the client root directory (next to mods and config), and copy it into config folder (.minecraft\config\MNMM\modlist.json).
* Keep in mind that the modlist.json file will contain all of your client's mods. It is recommended to keep only those entries that were mentioned in “Mod rejections” warning.

Copying from the server* (if there are many mods or have access to the server):
1. Start the server with MiniNoMissingMods and enter the “/MNMM modlist” command (it's case-sensitive).
2. Take the MNMM folder with the modlist.json file inside, generated in the server root directory (next to mods and config), and copy it into your client's config folder (.minecraft\config\MNMM\modlist.json).
3. Delete MiniNoMissingMods from the server. You can also delete the MNMM folder from the server.
* Keep in mind that the modlist.json file will contain all of your server's mods. It is recommended to keep only those entries that were mentioned in “Mod rejections” warning.

Server-only mode (if you have access to the server, and you don't want to configure anything):
1. Install the MiniNoMissingModsServer version on the server, and you can juggle the mods on the client as you wish. In this case, you don't need to install MNMM on the client, nor do you need to work with any MNMM files and folders.

Setting up, the basic version differs from the mini version in some ways.
First, you should create a config describing the mods you don't want to install on the client.

Manually (working only with the client):
1. Instead of MNMM folder, it's now NMM folder with a modlist.json file inside in your client's config folder (.minecraft\config\NMM\modlist.json), which makes sense. Also added here are the blocks (.minecraft\config\NMM\blocks) and items (.minecraft\config\NMM\items) folders, where you can define the matches of mod blocks to vanilla originals*.
* This means that you can define how a block or item unknown to your client will look on the server. In general, when automatically generating the NMM folder, the configs for items and blocks will be filled in automatically, but they will not include non-standard (not extended from vanilla) analogs. In this case, you can add such analogs to the corresponding config yourself; make a beacon from ThaumicBases Anvil or a pickaxe from IC2 Mining Drill.
2. The blocks and items folders will contain empty configs of supported vanilla blocks and items after the first run of the client. Their format looks like ["modid:item/block"]. For example, for AnvilsArray.json in the blocks folder, this would be ["minecraft:anvil"].

Automatically* (working with both client and server):
1. Start the server with NoMissingMods and enter the “/NMM all” command (it's case-sensitive). Actually, there are separate parameters for “blocks”, “items”, and “modlist”, but most of the time you only need “all”.
2. Take the NMM folder with the modlist.json file and the blocks and items folders inside, generated in the server root directory (next to mods and config), and move it into your client's config folder (.minecraft\config\NMM\).
3. Delete NoMissingMods from the server. You can also delete the NMM folder from the server.
* Keep in mind that the modlist.json file will contain all of your server's mods. It is recommended to keep only those entries that were mentioned in “Mod rejections” warning.

Q: Is it safe for the server/client?
A: It is absolutely safe for the server, there is no way to harm the server by NoMissingMods. The only thing to consider is that such mod features may not be to the liking of server administrators, where there are certain strict rules about mods.
For the client is dangerous only at the level of crash when interacting with some mechanics of mods. But this is predictable behavior, which will not be able to corrupt your files. And can be fixed over time.

Q: What can this mod be useful for and in what situations?
A: The primary goal of the mod is to help eliminate the mandatory (by the author's decision) installation of mods on the client in order to easily join servers that require them. A mini version of the mod is enough for this. The basic version of the mod can be used in any way, including partially disable some modpack mods, if this is a planned part of the gameplay. Such modpacks can consist of many small clients with a common server and develop independently, but with interaction between all players on the server. You can also disable any mods on the client (except for NMM itself and ASJCore, of course). This can be useful for critically reducing the load on the player's client, for familiarization purposes, or for testing, which requires a temporary disable of a certain number of mods.
 

Q: Can this mod be called a cheat?
A: In a way, it is possible, but it directly depends on the player's or administrator's evaluation. Nothing cheating this mod does not add or do intentionally.
 

Q: Will the mod work on <your launcher>?
A: Both versions of the mod are tested on MultiMC/Prism, Legacy Launcher and Gravit Launcher. If your launcher does not differ from these in the principle of operation, then there should be no problems.
 

Q: Does the mod have any incompatibilities or other issues with other mods? 
A: We are not aware of any incompatibilities. If you encounter a similar issue, be sure to let us know via the Issues section or our Discord server.
 

Q: Does the mod work in singleplayer?
A: The mod is originally designed for multiplayer, and use in singleplayer is not expected. But if you notice any interesting behavior in SSP, be sure to let us know ^_~