Is poesmoother bannable ?

I would like to use it to increase visibility

Yes, this modding-tool is 100% bannable.

You won't get an official answer from a dev for obvious reasons but the ToS is pretty clear on this.

"

7. Restrictions: Under no circumstances, without the prior written approval of Grinding Gear Games, may you:

b. Modify or adapt (including through third parties and third-party tools) the game client or its data, other than in the normal course of PoE gameplay as permitted in accordance with the Licence.

https://www.pathofexile.com/legal/terms-of-use-and-privacy-policy

What are the obvious reasons?

I see "other than in the normal course of PoE gameplay" so it is probably fine.

Also it says "without the prior written approval of Grinding Gear Games" so it seems they should give an official answer.

They can't "approve" 3rd party tools because these tools can completely change from one day to another and are fully outside of the control of GGG.

It's extremely vulnerable to being abused and exploited. It could also lead to being sued on all 3 sides (GGG, the player, the 3rd party tool creator).

"

SoulMule wrote:

Also it says "without the prior written approval of Grinding Gear Games" so it seems they should give an official answer.

It means they can hand out licences and make exceptions in situations like the chinese PoE version. That part has absolutely nothing to do with "can I use a clearly not allowed modding tool".

Also it is literally in their ToS. That's as official as it possible can be.

This tool goes against the TOS very clearly. Using third party software to edit the appearance of the game is definitely not "the normal course of PoE gameplay".

I do not recommend using this software. If you do, you use it at your own risk.