In vanilla Minecraft, there are the beginnings of a stealth system.
For example, mob detection range is reduced by 20% when the player is sneaking.

However, I thought this has little practical use in real gameplay, so I decided to make this mod.

New features:

Now there’s a reason to walk instead of run: while walking, detection range is reduced by 25%.
If the player is standing still or sneaking, detection range is reduced by 50% instead.
If a mob is facing away from the player, detection range is further reduced by 50%.
If the player is standing in tall grass, detection range is reduced by 50%.
New armor enchantment Stealth. For each level of the Stealth armor enchantment, detection range is reduced by 4%. Not compatible with the Protection enchantment.
The Invisibility effect reduces detection range by 93%, 82.5%, 65%, 47.5%, and 30% respectively when wearing 0, 1, 2, 3, or 4 armor pieces, just like in vanilla Minecraft.
Under the Blindness effect, a mob’s follow range is reduced by 50%.
If the player has the Glowing effect, stealth does not work.
If the player has attacked a mob within the last 10 seconds, stealth does not work against that mob.
Detection reductions stack with diminishing returns. For example, if the player is sneaking behind a mob, detection range is reduced to 25%. Calculation example: 1 * (1 - 0.5) * (1 - 0.5) = 0.25.
Also added attribute betterstealth:stealth, which is set to 0 by default and unused. This attribute reduces mob detection range (for example, a value of 0.2 means a 20% reduction). You can assign this attribute to rogue-class items in your modpacks.

All values are configurable

This mod does not change mob behavior and does not conflict with other mods.

Demi's Better Stealth