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Illegal castling

no it was legal. the king cannot pass through check but the castle can

Interesting, I'd never seen this. Thanks!

That is a legal castle.

When is a castle illegal?
* If the rook you want to castle has been moved
* If your king has been moved
* If you are in check
* If the squares which your king uses to castle are under attack

In your game the c8 and d8 squares were not under attack, allowing you to castle.

@mohamadreza1386 That's a "from position" game with long castling allowed for black. It's basically 960 castling in that game:
en.wikipedia.org/wiki/Chess960#Castling_rules

I can see that you've created that game. The black king is already castled, so if you want to continue a normal game, uncheck Black O-O and Black O-O-O on the board editor before continuing the game from the position.

@DoTheMath Yes, I was so sure that I knew the correct rule as "no square involved in castling, from king to rook included, should be under attack" (it's been about 30 years and I never encountered that rare situation where the difference matters), I didn't even read that castling article until the end... Thanks!

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