Mark5000's Guide to the Opening (v2)


Hello OGS. This is an update to the prior thread mark5000's Guide to the Opening. This lesson is intended for novice players who would like to understand high-level opening theory presented in an accessible way. This theory includes innovations of AlphaGo, which rendered the previous guide somewhat outdated. As before, I don’t claim to have any special knowledge about the opening. This is just a distillation of recent Go knowledge through the eyes of a Go lover and enthusiast. I hope it helps you understand the opening better.

OGS demo format

SGF for quick access and offline viewing

mark5000’s Guide v2.sgf (19.8 KB)

Please let me know if there are any errors or necessary omissions or any other thoughts you may have.


Thank you for updating your wonderful guide!

The impact of strong AI on opening theory sounds very interesting to me, however, perhaps I’m not strong enough to really appreciate what we may have learned from these bots. In what ways has AlphaGo most impacted our understanding of opening theory? Could you point out some specific examples where it has really changed the way we understand certain positions?

Sorry for the redundant questions if you already go into this in detail in your guide. I haven’t had a chance to work through it yet, but I am really looking forward it!


Sure. In my view, here’s what the key innovations are, and what’s changed from v1:

  • The axiom corners-sides-center is now just corners. Corners are more valuable than once thought, and splitting moves on the side have vanished. This means that opening play centers around the corners, after which strength and weakness of groups determines play more so than location on the board.

  • Named openings are dead. We all know there are a huge number of perfectly valid moves in the opening. But there was an effort, treated more religiously by westerners, to label certain openings similar to how chess openings are labeled, such as orthodox, Chinese, Kobayashi, etc. We now know these named openings are not special, and the AI-suggested “best” paths avoid all of them entirely. I preserved some of the lingo in the lesson, but mostly it’s back to the drawing board.

  • The 3-3 invasion reigns supreme. A consequence of increased value of corners is that the 3-3 point invasion of a 4-4 point is now a first-order move, just behind taking a corner in terms of priority. This means it can be played as early as move 3. The joseki have also changed, including the beginner-friendly bend-and-extend joseki, which now won’t give the opponent a hanging connection.

  • Answering a 4-4 point approach is just big not urgent. There’s new ways to handle the double approach of a 4-4 stone, namely by attaching on top of either stone. Since this gives a better result than once thought, approaching a 4-4 point can be gote, which is another reason why the 3-3 invasion has increased in popularity.

  • Enclosure popularity is reversed. Pro and amateur players used to choose the small knight enclosure of a 3-4 point more than any other enclosure. To everyone’s surprise, the two-point high enclosure is the preferred enclosure of all bots from AlphaGo to Fine Art to LeelaZero, and the small knight enclosure is the least favored one, being slightly overconcentrated and vulnerable to shoulder hits and attachments.


It’d be nice to have numbers marking all of the continuations for the OGS version. In the empty-board starting position, for example, marking the 3-3, 3-4, 4-4, 3-5, and 5-4 would be a nice visual indicator of what the different branches are. There’s a few instances where some, but not all, of the lines are labeled with letters in OGS, such as after white plays the far corner, where black’s near corner responses are marked but the diagonal is not.

The eidogo SGF sort of does this, but transpositions aren’t marked. For example, black and white play hoshi in opposite corners, and black follows up with nirensei, there’s no marked continuation. Playing the last hoshi transposes back to a commented line, but having a visual indication of that would be nice.

Also, not sure why, but I get a different variation if I open up your review vs. if I download the SGF. The downloaded one seems like it has more variations, and is likely the “v2” version of the guide.


I hear you. It’s mostly a shortcoming of OGS. When you download a demo SGF from OGS, that SGF contains all branches ever created in the demo, even if you deleted them. It also sticks with the original branch ordering, even if you reordered them in OGS. I had to download the SGF and then manually prune the branches I deleted in OGS, but it still doesn’t match perfectly. I’m not sure what to do about that.


Thank you making this list. I have often heard people remark generally and vaguely about how the bots are changing our understanding of opening theory, but I have never seen such a clear and descriptive list of prominent examples. I was unaware of the scale and nature of the impact, and your list is very helpful to me.


I have always, instinctively been especially keen on taking and keeping corners. I feel validated by this information. Is it accurate to say that the bots also emphasize a territorial game rather than an influence/moyo game?


@mark5000 Great summary of the recent evolutions in opening theory!


Something I struggle with is the question “does this knowledge apply to me (a solid DDK)?”.

For example, when the 3-3 invasion thing first started hitting, Dwyrin said basically “that’s nice if you can do whole board reductions skillfully, otherwise maybe not, for us mere mortals”.

Is that still the thinking? Or is the knowledge of what to do with these innovations getting well enough understood to pass down the ranks?

I suspect there’s something similar with two-point-high 3-4 enclosure preference. That might be important if your opponent is accomplished at attachment play … but are they? Is the bot-perceived drawback of low knight not actually applicable at DDK level of play?

At the meta level, this is a topic I’ve been interested in for some time: the question of how real and significant “stratification of strategy among ranks” is. It became more interesting with AIs, because they far extended the spectrum of strata…

I don’t see much in the way of formalisation of this in Go teaching and thinking - the tendency is more towards expecting that “a good move is a good move”. I’m not at all sure that’s true, and I suspect that at some point our approach to training may stratify more…



I don’t think so. AI has stunned us with both bold invasions and bold fifth line plays.

As I have mentioned in another thread, the simple fact that they favor the 4-4 point in the opening and allow for a 3-3 invasion shows that they are not too territory oriented.

Just to be clear, @mark5000 never talked about keeping corners. “Corners are more valuable” should not be interpreted as taking corner territory.