How should I have played against this opening?

Against an unusual line, I always fail because I have no idea what I am doing. I would like to know how I should have played against this. The game was 30+0, but time wasn't a factor because I lost so quickly. I have not done the computer analysis.

My intuition is that 3. h3 is an extremely slow move that only helps white if you wanted to play ...Bg4 or ...Ng4 at some point. But because the move is so slow, you should consider breaking in the center with ...e6 and ...c5 (or just the immediate ...c5, even). Once you break open the center, you should be at least equal, as white won't be ahead in development.

At some point, you needed to play ...Ne4. You can play this move because you haven't moved your e-pawn yet, and it's also good because it gets out of the way of your DSB. Any time you play ...Bg7, you also want to find a way to get your Nf6 out of the way, and you want to find a way to play ...c5, so actually I think 8... c5 is fine here. On 9... Ne4 10. Nxe4 dxe4 11. Nd2 cxd4, I think black's position looks just fine. Engine says that black's position is slightly better, even.

But I think those were the two key ideas I saw out of the opening: (1) when your opponent plays a really slow move, you should consider punishing it either by getting a lead in development or by breaking open the center; (2) when you fianchetto a bishop, part of your middlegame plan needs to be focused on getting scope for that bishop (in this game, that's via ...c5 and ...Ne4).

@1
3...e6, 3...Bf5, 3...c5 all make sense to profit from his tempo loss 3 h3.
6...c5 was stronger than 6...c6. With 6...c6 you drive his Bb5 to a better square and you block square c6 for your own Nb8 and you will have to play ...c5 sooner or later anyway to contest hist center. 6...c5 right away was strong. His Bb5 is misplaced. You can even trap it with ...c4, ...a6, ...b5.
Not of course 6...Bd7, only playing into white's hand.

There's nothing wrong with 6. ... c6.

What you NEED is not a specific sequence of moves, but a plan of development.

The position is semi-closed. Your light-squared Bishop appears to have no useful square. There is no particular hurry, and you can afford to take your time and maneuver a bit in order to get your pieces developed to effective squares.

In theory, c7-c5 will be an excellent move. In practice, it somewhat weakens your d5 square. So my own impulse would be (in the short term) to over-protect the d5 square, with the intention (in the long term) to play c5 after my d5-Pawn is safe.

So I would have played c6 (over-protecting the d5 square and the light squares generally) and followed it up by using the Nest Method... playing Nbd7, then b6 (creating the Nest), then Bb7 (fianchettoing the Bishop BEHIND the c6-Pawn), optionally Rc8, and only AFTERWARD play c6-c5.

You might complain that this maneuver loses a tempo by playing first c7-c6 and later c6-c5... but the center is semi-closed. In such positions, the loss of a tempo is trivial compared to putting your pieces on the proper squares.

Here's an illustrative sequence of moves... just to give you the general idea:

blueemu - this ain't my thread, but thanks for this post. I haven't seen this method before, and this idea of spending a tempo for overprotection in a closed position... very logical. Thank you!

I also think the c6 is fine.

However, it is interesting that you mention 3 mistakes, and those not include 13. - Qxc5. Instead, 13. - Bxc3 14. bxc3 Qxc5. That way you keep the d5 pawn, and white's pawn structure is ridiculous. If anyone is better in this position, it must be black.

@4
6...c6? 7 Bd3 Nbd7 8 Nf3 b6 9 Ne2! (prophylaxis: prepares against ...c5) Bb7 10 c3 is just equal.
Therefore 6...c5! is much stronger and refutes 5 Bb5?

Hi, i checked your game and put my comments on it. Forget computer analysis and evaluations! Proper assesment and planning is of highest importance!

You will see that we are both mismatching in many of views, many your moves which you think were bad, I would say they were not, again let us not go with computer analysis because we do not use them during the game.