most effective way to do it is teleporting them into the void when they appear, its not really preventing them from spawning but effective it removes the mob from the game.

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put this in a command block set to unconditional, allways active and repeat and replace creeper with whatever mob you want to remove.

/teleport @e[type=minecraft:creeper] ~ ~-5000 ~

High light levels prevents most hostile mobs, other than that string, slabs or carpet on the ground can prevent most spawns.

i use a command block. i built a cool underground base in my new world, turns out it's a slime chunk. my base is always full of slimes bouncing around. i got so annoyed with it i just put a slimeblock, i use the teleport method (you can /kill them, but then their drops will be all over the place, and having my inventory always filling up with slime was one of the problems i was trying to address!). so i just run /tp @e [type=slime] 0 -10 0. they teleport underneath the bedrock and fall into the void.

if you place this in your spawn chunks it will be dimensionally-active meaning that wherever you are in that same dimension, the command will be running.

if you place them in non-spawn chunks they will be activated by proximity. if you are near enough the command block to load it, all entities of that type will teleport. if you are too far away and the command block is not loaded, no entities will teleport.

What mob are tou trying to prevent?

Depends on which mob you not want to spawn

Don’t know of one yet but i will keep lookin for ya, have the sameee problem, safe moding!

/gamerule doMobSpawning false

if you build a mobswitch, spawners shouldn't be affected.

https://www.youtube.com/watch?v=J6gtmxOyO_E this one by Fortun8Diamond is very easy to set up

Could build a Mob switch in your spawn chunks.

try /gamerule doMobSpawning false (im assuming u can use commands if u have spawn eggs) not sure if it affects eggs or spawners

Any non spawnable surface would work. Glass, slabs, leaves etc.

Have you read the wiki ?

Since the syntax is different in different versions you would have to say what Minecraft version you’re on.

Also try the discord, they are friendly and will help you if you ask.

Higher Vanilla difficulty levels will spawn more mobs at once.

in control is good for controlling what mobs spawn and how many of them. But it does take work.

I believe theres a mod that simply boosts all spawns of all mobs but i cant think of the name off the top of my head. Ill try to find it.

Use torches

Could use glowstone or redstone lamps as they look nicer. Or just use peaceful mode and turn it off when u want to fight

Peaceful mode?

either use slabs or make a huge carpet with light under it

Put slabs or glass there

you would need to go to every single block and F3 to see what the light level is (assuming you have Java... if you're bedrock like me, idk how to tell). if it is too low, you need more light.

edit: like mentioned in another comment, you would need to check every block, including those on roofs, your outer walls, the tops of trees, and so forth. inside the houses too of course :)

Maybe there's somewhere a hole in the wall or the mobs spawn on the wall and fall down?

Make sure your roofs and the top part of the outer wall has light, and preferably don't have trees in the village, it is not easy to light them up.

just sleep every night

I don’t believe you have enough light if there’s mobs spawning everywhere. If you have enough villagers, they will build iron golems to protect them. And if you have enough light, only a very small amount of mobs will spawn. Try turning your brightness down by half, and then look at how much darker it is. They physically can’t spawn past a certain light level, so it’s definitely the light .

Change the minimum and the maximum to 1, the attempts down, and the per second way up. Maybe like 5 spawn attempts once a day might get you there. It'll require tweaking though because it depends on other mobs spawning conditions.