How do I know when I mastered an opening?

How do I know when I mastered an opening?

I've been playing the nimzo larsen for almost a year now (or even more I don't remember)

But I don't know if I mastered it

I never really studied it except for a yt video and a little bit of preparation

But have I mastered it

I usually know what to play and get good positions or atleast even positions

The same goes for my other main opening which is the KID

But sometimes I get caught off guard when my opponent plays something new (this happens very rarely)

Now that I think of it what is mastering an opening

Is it simply knowing every single possible line

Or is it having experience and being able to easily play it and know most lines and play it quickly

Play it ten times against a GM and win at least eight games. Then you mastered it.

@sheckley666 said in #2:

Play it ten times against a GM and win at least eight games. Then you mastered it.

GM? Someone your level is better.

@sheckley666 said in #2:

Play it ten times against a GM and win at least eight games. Then you mastered it.
Im assuming this is sarcasm but while I may be able to get away with an equal opening Im gonna get crushed in the middlegame and endgame (assuming I even make it that far)

@Kyrylokkk said in #3:

GM? Someone your level is better.
While someone my level is better it still doesnt change the fact that I could do bad in the middle/end game
Maybe changing the goal from winning to getting a good or atleast even position would be better but still idk for sure If I mastered it

@venter4971 said in #1:

... Now that I think of it what is mastering an opening ...
"... I am not a big fan of weaker players memorizing lots of opening lines they will never play. However, it is quite a different issue to spend a small amount of time learning how to play your openings a little better each time they occur. A long journey begins with a single step. ..." - NM Dan Heisman (2005)
https://web.archive.org/web/20140627023809/http://www.chesscafe.com/text/heisman50.pdf

You cannot truly master an opening until you beat the World's best players with it, as they will provide the strongest possible refutations.
Modern online titled players have played tens of thousands of games (or absorbed the positions over long classical games) & thus spend less time calculating as they've been around the block many times :)

First off I played the NL myself for about a year and it made me a worse chess player, so I recommend that you play something else tbh. If you really want something similar, then 1.c4 will do you much better. Just make sure you have a little prep for 1.c4 e5 and 1.c4 c5 and you should be good to go.

As for beating masters, that proves that you've mastered chess, not an opening. Someone can understand his opening well and still not be able to beat a master because such a feat is not within reach of his general chess skills. IMO you've mastered your opening when you have an overwhelmingly positive record against peer strength opposition in the opening, both in mainline positions and made-up nonsense.

You can look at the opening explorer and see your performance in the opening.

'I usually know what to play and get good positions or at least even positions'

In the classic book, 'How to open a chess game', Lajos Portisch says 'Your only task in the opening is to reach a playable middlegame.' If you're getting good or at least even positions, even a GM will envy you.

'But sometimes I get caught off guard when my opponent plays something new (this happens very rarely)'

You're going to get out of book at some point in every game. Your experience will give you intuition on what the right move or plan is.

'But have I mastered it'

Easy to find out. Are your opening moves the same as an engine's? Or the popular choice of humans, especially GMs, who reach the same position?