Search depth
Search depth is how many moves ahead an engine has looked in a position, counted in half-moves called plies, and deeper searches generally give more reliable evaluations and moves.
In practice: glance at the depth before you rely on a score.
Also called: depth
Search depth tells you how far into the future an engine has calculated. It is counted in plies, where one ply is a single move by one side, so a depth of twenty means ten moves by each player. Analysis boards display the depth beside the evaluation, and it rises as the engine thinks for longer.
Greater depth usually means a better result, because the engine has seen more consequences of each move. Early in a search the top move can change as the engine finds a tactic that was beyond its horizon. Once the depth has grown and the best move stays steady, you can trust the suggestion more.
As a student, glance at the depth before you rely on a score. A quick glance at depth 10 may miss a deep combination, while depth 30 or more on a quiet position is quite dependable. Engines also extend important lines, such as checks and captures, further than the stated depth, so the number is a rough guide and not an exact limit. Give the engine a few seconds on critical positions, and do not draw firm conclusions from a very shallow reading.
It sits close to Principal variation. The principal variation is the line of best play for both sides that an engine has found, shown as a sequence of moves and tied to the evaluation it reports.
A neighboring idea is Minimax. Minimax is a decision method in which one side tries to maximize the evaluation while the opponent tries to minimize it, forming the basis of how traditional chess engines choose moves.
Compare it with Alpha-beta pruning. Alpha-beta pruning is a search technique that skips branches of the move tree that cannot change the minimax result, letting engines look much deeper using the same amount of computing time.
Computer terms such as "Search depth" are most useful next to a coach who reads your games with you, which is how a first lesson with George Li works.
Related terms
The principal variation is the line of best play for both sides that an engine has found, shown as a sequence of moves and tied to the evaluation it reports.
Alpha-beta pruning is a search technique that skips branches of the move tree that cannot change the minimax result, letting engines look much deeper using the same amount of computing time.
Minimax is a decision method in which one side tries to maximize the evaluation while the opponent tries to minimize it, forming the basis of how traditional chess engines choose moves.
A chess engine is a computer program that searches positions and evaluates moves, usually playing and analyzing far stronger than any human, and it is used for analysis, preparation and play against a machine.
An evaluation is a numerical judgment of who stands better in a position, usually given in pawns from White’s point of view, where positive favors White and negative favors Black.
Engine analysis is the use of a chess program to search a position and report which moves are strongest, along with a numeric evaluation and the lines it expects both sides to follow.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
How much does chess coaching cost?
Published rates for private, group and subscription chess coaching, with the source and the date of each.
A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.