What is a book move in chess?
A book move is an opening move from theory, already played and studied by strong players. It tells you the line is known, not whether the move is good.
A book move is a move from opening theory. Strong players have played it, written about it and analysed it, so the position after it is known territory. In a game review the first moves of most games get the book label, and the interesting part starts when one of you leaves it.
What does book mean in chess?
The name comes from opening books, the thick volumes that list the main lines of every opening. Today it means any opening move that is part of established theory. Chess.com calls it a conventional opening move.
Two related phrases you will hear: a player who is out of book has left the known lines and is now playing on their own. A novelty is a new move in a known position, one that theory hadn’t seen before.
Does a book move mean you played well?
Not really. Book only tells you the move is known. Theory includes dubious lines and traps that are there precisely because so many people have fallen into them. And in most opening positions several moves are book at once.
| Label | What it tells you |
|---|---|
| Book | The move is known opening theory |
| Forced | It was the only legal move |
| Best | It was the strongest move in the position |
| Blunder | It threw the game away |
Book and forced describe the move. The other labels judge it. For the full scale, from brilliant to blunder, see the articles on each end.
Why is a strange move marked as book?
Because somebody played it and it got studied, sometimes exactly because it sets a trap. Every site also keeps its own book. Chess.com rebuilt its own in 2023 and took bad moves out of it. So the same move can be book on one site and not on another, and the odd gambit your opponent played may be in one book and missing from the next.
What do “last book move” and “out of book” mean?
The last book move is the last one still in known theory, and out of book is everything after it. From there on, the review stops calling your moves book and starts judging them. Chess.com puts it this way: the first key move is usually the last book move.
Leaving book is not a mistake. Someone always leaves it first, and what counts is the move you play after. A game review marks the last book move of every game, so you can see where your preparation ended.
What does leaving book look like?
There are two ways it goes. Someone leaves with a sound move and the game goes on, or someone leaves with a mistake and gets punished. The game at the top of the page is the second kind. Here is the first.
Leaving book with the best move
What does forced mean?
A forced move is the only legal move in the position. There is nothing to choose, so there is nothing to judge, and a review marks it as forced instead of grading it. It usually happens after a check, though not every check leaves only one move.
The only legal move
Don’t mix it up with a forcing move, which is a check, capture or threat that forces your opponent to respond. In annotated games, □ marks the only reasonable move, which is a wider idea: there may be other legal moves, they just all lose.
Does Lichess mark book moves?
No. Lichess’s analysis only marks inaccuracies, mistakes and blunders. To check whether a move is theory there, you open the opening explorer, which shows what masters and Lichess players have played in the position. Chesslord marks the book moves in your Lichess games too.
How long should you stay in book?
As long as you understand what you are playing. In club games, theory usually runs out early: your opponent plays something you haven’t seen, or you forget the next move. What helps then is knowing what your opening is trying to do. Remembering ten more moves won’t help you once you are on your own.
- Know the first moves of your openings and what they are for
- Learn a few moves of each line you play, and why they are played. Then when your opponent plays something new, you still know what you were aiming for.
- When your opponent leaves book, look for what they left behind
- A move outside theory is often a move that forgets something, like 2...a5 above. Check what it no longer guards before you carry on.
- When you leave book, play by the position
- Once you are on your own, stop trying to remember and start looking: develop, castle, and check every capture.
- Look back at where your games leave book
- If the same opening keeps getting you into trouble two moves after theory ends, that is the line to study next.
Chesslord’s insights show how long your games stay in book, opening by opening, and who leaves it first.
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