How much opening knowledge is essential?

I recommend a basic openings manual for your openings needs. Just study the opening and variation you wanted to be part of your repertoire. Fundamental Chess Openings by Van Der Sterren

The answer is really very little.

To put it another way, how far do you go before you are normally out of book in your games? And how much of how far you do go could be covered by basic opening principles. There is no point to learning stuff 10 moves deep if you are typically out of book by turn 6 or 7.

I would suggest going for classical openings e4-d4 and knowing the main lines for like the 10 moves. Then checking some sides lines.

I think you are trying to solve a problem which doesn't exist.

Opening knowledge of any amount is not essential.

Whenever it is your turn to move try to play a great move.

https://web.archive.org/web/20140626173432/http://www.chesscafe.com/text/hansen128.pdf

http://www.jeremysilman.com/shop/pc/FCO-Fundamental-Chess-Openings-76p3561.htm

http://www.gambitbooks.com/pdfs/FCO_Fundamental_Chess_Openings.pdf

I would strongly recommend examining the sample. I do not remember seeing much in the way of sample games.

"... Overall, I would advise most players to stick to a fairly limited range of openings, and not to worry about learning too much by heart. ..." - FM Steve Giddins (2008)

"... I feel that the main reasons to buy an opening book are to give a good overview of the opening, and to explain general plans and ideas. ..." - GM John Nunn (2006)

"... If the book contains illustrative games, it is worth playing these over first ..." - GM John Nunn (2006)

"... the average player only needs to know a limited amount about the openings he plays. Providing he understands the main aims of the opening, a few typical plans and a handful of basic variations, that is enough. ..." - FM Steve Giddins (2008)

"... Everyman Chess has started a new series aimed at those who want to understand the basics of an opening, i.e., the not-yet-so-strong players. ... I imagine [there] will be a long series based on the premise of bringing the basic ideas of an opening to the reader through plenty of introductory text, game annotations, hints, plans and much more. ..." - FM Carsten Hansen (2002)

https://web.archive.org/web/20140627055734/http://www.chesscafe.com/text/hansen38.pdf

"The way I suggest you study this book is to play through the main games once, relatively quickly, and then start playing the variation in actual games. Playing an opening in real games is of vital importance - without this kind of live practice it is impossible to get a 'feel' for the kind of game it leads to. There is time enough later for involvement with the details, after playing your games it is good to look up the line." - GM Nigel Davies (2005)

"... Review each of your games, identifying opening (and other) mistakes with the goal of not repeatedly making the same mistake. ... It is especially critical not to continually fall into opening traps – or even lines that result in difficult positions ..." - NM Dan Heisman (2007)

https://web.archive.org/web/20140627062646/http://www.chesscafe.com/text/heisman81.pdf

Memorize the first 5 moves (or so) of the main lines.

Other than that play a lot of games (and check your moves vs a database) and play over a lot of GM games from the openings you like.

You have to memorize some moves, especially for sharp openings, but if you actually understand why the moves are played, they'll be easier to remember and will stay in your memory longer. For that you just need experience (studying chess in general, playing games, and looking at games). I'd say opening books aren't necessary at all.

Ok maybe it's not essential, but that's misleading. Anyone can improve their results by switching from dubious openings played on a whim to openings based on good principals where the first few moves have been memorized.

Some of them are mostly sources of games with explanations intended for those just starting to learn about an opening.

"It is important for club players to build up a suitable opening repertoire." - GM Artur Yusupov (2010)

I honestly got better after learning Queen Gambit accepted and declined variations in detail. For Black, i still have a lot to study about the Najdorf, but I like it already.

In the age of 2000s chess, there are Encyclopedia of Chess Openings, Powerbooks, etc. They are too much for most chess enthusiasts. An openings manual is more than sufficient. You can add your personal notes and highlights important variation and sub variation.

Some us find book explanations helpful.

The most important thing is to be efficient when learning openings. The use of spaced repetition (as offered in Chessable and some few other websites or programs) will assure that your opening study will be effective.

This effectivity will allow you to invest most part of your time in learning tactics. I would say that you should invest only 20 % of your training time in opening, 70% in tactics and the rest on basic endgames (I didn’t include the analysis of your own games, as this will take again a lot of time).

I was not doing this in the past, but in 2019 I will change this. At least I have already a basic repertoire with white, so I need only few minutes per day to review this opening. My main problem is still to defend against 1.d4 and other moves like the KIA, 1.b4, 1.g4, 1.b3 etc.

My goal in 2019 is to do at least 30 minutes on tactics 5 days in the week, and at least twice as much in the other two days.

Yeah, right! Lol 😆

My advice is: if you read The Ideas Behind the Chess Openings originally written by Reuben Fine in 1943, you never have to study any other openingsbook again. Of course, after reading this book, you still can study openings in more detail if you want, but then at least you will have a solid foundation. 

It’s more important to understand typical patterns in an opening than remember book moves. AFAIK most games below 2000 or so don’t follow the book for more than 10 moves. You should have a general idea what you’re going to do once the game deviates from known territories.

Let’s say you are a Ruy Lopez player. After 1. e4 e5 2. Nf3 Nc6 3. Bb5 your opponent tosses out 3..Nge7 (not a bad move). what would you play? You might not know the book lines, but if you know typical patterns in the Ruy Lopez (fight for central space with c2-c3 and d2-d4, in this case) you’d be able to figure out good moves like 4. O-O g6 5. c3 a6 6. Ba4 Bg7 7. d4 all on your own. Patterns like this is what a good opening book teaches you.

 

Edit: a move.

Rhe book is indeed good. The problem is that if you compare what he wrote with a concrete repertoire book you will see that a lot of lines are not considered, of course. It is a book for somebody who still doesn't know what to play and need an orientation about which kind of opening he wants to learn.

My advice was meant for a 1700-player. 

Your blitz rating here is 1300 and bullet is 1100. So you are more likely 1200. (You probably have online 1700 in another bogus site like chess 24) 

Accept the right right fact first, and then ask opinion for the right level.