The test
Does it give you something a player with the same client cannot have?
If yes, it is banned. That single question answers almost every case, and it
answers them the same way we would.
Fine
- Optifine and performance mods generally.
- Minimaps — without an entity radar. The map is fine. Seeing players and
mobs through terrain is not.
- Schematica — without the printer. Showing you a plan is fine.
Placing blocks for you is not.
- Sound, interface and quality-of-life mods that do not tell you anything
new about the world.
Banned
- Killaura, aim assist, reach, any combat automation.
- Fly, speed, no-fall, anything that changes movement.
- X-ray, cave finders, ore highlighting, entity radar — including a texture
pack that does it, which counts exactly the same.
- Auto-clickers and macros. Including for "just fishing".
The pattern in the exceptions
Two of the allowed mods have a banned half — the minimap's entity radar and
Schematica's printer. That is not arbitrary. In both cases the base mod shows
you what you could already see, and the banned half either reveals hidden
information or takes an action for you.
Apply that split to anything not on this list and you will usually get the
right answer.
"I was just testing it"
We cannot tell that from the outside. Neither could the person you were
fighting. Trying a hacked client on the server is using it, and it is treated
that way.
When in doubt, ask first
On Discord, before you install it. A question costs nothing and gets answered
in a minute. A ban costs your account, and "I asked and was told it was fine"
is a defence that only works if you actually asked.
Texture packs
Same test. A pack that makes ores glow through stone is X-ray with a different
file extension.
Reporting somebody
If you think someone is using something banned, report it while they are
online — that is when it is catchable. A video is worth far more than a
description.