How To Use The Incontrol Minecraft Mod

First, add the mod to your server. If you are running an existing modpack, it may already exist
https://www.curseforge.com/minecraft/mc-mods/in-control

Once you boot the server once with it on it will load its files

Managing Existing Spawns

The existing spawns can be managed in spawn.json
config > incontrol > spawn.json

Basic spawn Limit

This rule limits each mob type to a maximum of 50 of each mob

{

       "dimension": "minecraft:overworld",
       	"mincount": {
        "amount": 60
      },
      "result": "deny"
 }

• Dimension - The dimension this rule applies to.

• mincount - The maximum allowed spawn count.

• Amount - The number of mobs allowed.(Unless defining mob ,this will be 60 of each mob)

• Result - Determines the outcome when the limit is reached. Setting this to "deny" will prevent further mob spawns past the limit

Per player

This setting scales mob spawns based on the number of players online.

{
       "dimension": "minecraft:overworld",
       	"mincount": {
       	"perplayer": true,
        "amount": 50
      },
      "result": "deny"
 }

• perplayer - If true, the mob limit is applied per player.

• amount - The number of mobs allowed per player.

Block certain Mobs

You can block certain mobs from spawning, which is useful if one type is taking up too many spawn slots.

 {
       "mob": ["minecraft:pig","minecraft:chicken"],
       "onjoin": true,
      "result": "deny"
  }

• mob - A list of mobs to restrict. Use their in-game ID, which can be found using the /summon command. Follow the format in the example: ["mob1", "mob2"].

• onjoin - If true, the rule takes effect when the world loads.

Adding new spawns

config > incontrol > spawner.json

[
  {
    "mob": ["minecraft:sheep"],
    "persecond": 0.1,
    "attempts": 25,
    "amount": {
      "minimum": 1,
      "minheight": 45,
	  "seesky": true,
"block": ["minecraft:grass"],
      "maxheight": 75,
      "maximum": 1
    },
    "conditions": {
      "dimension": "minecraft:overworld",
      "maxthis": 10
    }
  },
  {
    "mob": [ "minecraft:chicken"],
    "persecond": 0.1,
    "attempts": 25,
    "amount": {
      "minimum": 1,
      "minheight": 45,
		"seesky": true,
"block": ["minecraft:grass"],
      "maxheight": 80,
      "maximum": 1
    },
    "conditions": {
      "dimension": "minecraft:overworld",
      "maxthis": 10
    }
  },
  {
    "mob": ["minecraft:cow"],
    "persecond": 0.1,
    "attempts": 25,
    "amount": {
      "minimum": 1,
      "minheight": 45,
		"seesky": true,
"block": ["minecraft:grass"],
      "maxheight": 80,
      "maximum": 1
    },
    "conditions": {
      "dimension": "minecraft:overworld",
      "maxthis": 10
    }
  },
  {
    "mob": ["minecraft:pig"],
    "persecond": 0.1,
    "attempts": 25,
    "amount": {
      "minimum": 1,
      "minheight": 45,
		"seesky": true,
"block": ["minecraft:grass"],
      "maxheight": 20,
      "maximum": 1
    },
    "conditions": {
      "dimension": "minecraft:overworld",
      "maxthis": 10
    }
  }
]

This is a basic spawner file. This adds spawning for vanilla mobs. In this, it will have vanilla mob spawns on grass, must see the sky, can spawn a max of 10, Aswell as limits to hight

Mods wiki

Different Minecraft versions may have slight variations in functionality. Check the mod’s wiki for version-specific details, additional examples, and other configuration options: https://www.mcjty.eu/docs/mods/control-mods/