Is this considered cheating?

If I try to find a new game and lichess find me a game and I open the opening explorer( I open explorer in that 30 seconds BEFORE the game starts) to quickly check what opening my oponent plays, is that considered cheating? I guess not because it's just like a quick preparation for the oponent BEFORE the game(because I still didn't made any move), but just want to check.

Yes, I would consider it cheating.
If you're Black the opponent plays the first move and you look for that.
If you're White it is cheating as well: you already know you will play as White and you can check only those openings. Not mentioning you could check the opponent's account and see which openings he plays...

Ok, I understand your point but: " you could check the opponent's account and see which openings he plays" isn't this a common thing when you know who do you play and it's basically just preparation?

Preparation is BEFORE the game, not DURING. During it's CHEATING. Not a serious form, but yeah, it's cheating, it gives a little advantage.

there isn't a lot of time to check his preferred openings and study them in the explorer before the first move, but if you can and close the explorer BEFORE the first move it would not be cheating. Just opponent research.

But it may result in 'failure to start in time' playbans while you're looking things up, and if opening explorer is still open while you play it would be cheating.

@cormacobear Thank you for your respose. I see you are lichess moderator so I will consider your respose "official". :)
Actaully I just need simple things. I am an e4 player and wanted to start playing d4 as white. But I currently don't have time to study whole d4 repertoire so I thought it would be ok for me to learn to play against 1...Nf6 and if my oponent respond 1...d5 then I should stick with my e4 repertoire and not play d4. It is not hard to check that in 20 seconds.

Is this research also allowed when I am black? For example, lichess find me a game, my opponent instantly plays 1. e4. Can I open his profile when he already played his first move but I still didn't played my first move?

I read TOS now and it sais: "We prohibit the use of any external assistance used whilst a game you are involved in is ongoing, which has the effect of improving your knowledge, calculation ability, or otherwise gives you an unfair advantage over your opponent." But it seems like using an opening explorer is an external help, right?

Or maybe it make sense that I can use opening explorer if I am white because game don't even started but I cannot use opening explorer when I am black because my oponent already moved and that means that game already started?

If you have a match set up where you know your opponent, and that match is tomorrow, there is nothing wrong with looking at his normal opening repertoire, and of course he can look at yours.

Also, if there is a themed opening tournament coming up, you can do your prep on that opening. Or even when the arena is live, but you are not playing in it at the moment, you can do a bit of prep on the opening.

Once you are in a live game you cannot use any kind of analysis or have printed notes in front of you on the various lines. e.g. doing a chessable course and writing down all the lines and looking at them in a game = cheating.

yeah but if DURING the game you use opening explorer u will probably get banned

Well, I sometimes click on the username to see their profile (check their different ratings when playing on the tablet - which doesn't show the little popup with different ratings). So I guess I could also scroll through their recent games and get that (very basic) information.

But personally, I wouldn't do this. I consider the game started, when we're "at the board". It only distracts from the game, and it will often not be very accurate anyway. Imagine sitting at the board OTB, your opponent presses the clock, and you browse their games on a mobile phone. ;-)

You can play in scheduled tournaments, like the lichess4545 leagues. There, you know your opponent up front and can prepare, similar to an OTB game. Actually, you probably have much more information here than against most offline opponents.