castle-ing (castling?)

Castle when you have no better move.

The bias toward castling K-side is because it puts the King on g1, with a short front to defend (f2, g2 and h2). Castling Q-side puts the King on c1, with a somewhat longer front to guard (a2, b2, c2 and d2).

Castling Q-side does have the advantage that the Rook ends up on a central file (d1, instead of f1) but the King is less securely placed. So the usual consensus is that 0-0 is basically a defensive move while 0-0-0 is basically an attacking move.

Let’s take a look at when it makes sense to castle opposite sides and when it doesn't.

You should castle on the opposite side when at least one of the following factors is true:

1. When you are up in development and your opponent has already castled, you should consider castling in the opposite side. That way you will have a clear game plan and will also be able to capitalize on your development advantage.

2. When you have a damaged pawn structure (doubled paws, missing pawns, far advanced pawns, etc.) on one of the sides you should consider castling on the other side.

3. When opponent’s pieces are especially active on one side of the board, it is usually best to castle on the opposite side.

4. If you want to complicate the game you may consider this option. That may be true if you must play for a win due to a tournament situation, when the draw is not enough. Also that maybe done when you're playing against a stronger opponent, who is much better in simple/technical positions. That maybe your best bet.

You should not castle on the opposite sides when at least one of the following factors in true:

1. When you are behind in development and you need extra time to develop your pieces, it is usually not a good idea to give your opponent a straight forward way of launching an attack.

2. When the opponent’s pawns are advanced towards the side you’re about to castle, it is not a good idea to castle there (especially if the opponent’s king is castled on the opposite side). It will just give him a positional edge in the attack.

3. When there are open/semi-open files in-front of the side you’re about to castle, you should probably reconsider your decision to castle there (especially if your opponent has castled on the other side). That will give him more attacking possibilities, such as rook lifts, various sacrifices, doubling of pieces on the file, etc.

4. If you playing against a weaker opponent you may want to avoid castling opposite sides, in order to avoid sharp game and keep everything under control.

Note: These are general rules, not laws, meaning that there are always exceptions to them. When you’re making a decision what side to castle you should always take your time and evaluate all “pros” and “cons” and base your decision upon your own analysis. This is a very important decision. It pretty much dictates which way the game will continue. Take your time and think twice.

Castling allows you to move 2 pieces at once.

It protects the king, and activates the rook.

New players usually wait until it's too late to castle, also positions in which it's possible to punish a player for castling too early happen much less frequently than positions where castling late can be punished... all this together means it's safer to error on the side of castling early.

In the starting position the pieces are both passive (which you can think of as immobile) and also unorganized. The opening is all about mobilizing and organizing your pieces as quickly as possible. If your first 10 or so moves do this and your opponent's don't, then your position will objectively be better... sometimes even objectively winning.

Castling is part of this process, and you can castle kingside faster than queenside since there are only 2 pieces in the way vs 3 on the queenside. Plus 0-0 puts your king on the knight file vs 0-0-0 putting your king on the bishop's file. The knight's file is safer because e.g. the c1-h6 diagonal hits the 0-0-0 king, but there's no equivalent diagonal that menaces the 0-0 king. Also 0-0 keeps all 3 flank pawns on that side defended.

Often, if you wait until you "need" to, it's too late. Castling doesn't fight against an initiative, it's a purely preparatory move, so by the time your opponent develops threats it's usually too late.

In closed positions it's fine to delay castling... sometimes it's even a mistake to castle!

But this is the exception not the rule. If a new player is safe 9 times out of 10 by castling during the first 5 moves, then the best advice to give them is to castle during the first 5 moves.

Opposite side castling leads to middlegames where both sides go all in on attacking each other's king, usually with a "pawn storm" (advancing the pawns on that flank towards the enemy's castled king). Pawn storms trade pawns which opens files, ranks, and diagonals i.e. this is said to "open lines."

Since castling queenside takes an extra move, it's more common for white to castle queenside than black (white starts out 1 move ahead so it's not as much of a cost as it is for black).

Also when 0-0-0 your rook lands on the center file, so that's a little more active than landing on the f file as is the case with kingside castling.

It takes longer, the king is more exposed, and the rook pawn on that flank is not defended.

0-0 usually requires the extra move rook to the d or e file because it doesn't stand well on f1 / f8.

0-0-0 usually requires the extra move king to the b file because the king is more exposed on c1 / c8 and the a pawn is undefended.

So in summary, 0-0-0 yields slightly more piece activity at the cost of being slightly slower, and slightly less safe. 0-0-0 also tends to lead to more dynamic middlegames.

You can also view this quick 5 minute course on the site which talks about castling.