Tactical Mode (checkbox)

Activate tactical mode threads,

Default is 0, min 0, max 8 (Standard) or 128 (Pro)


0 = no tactical mode

1 = all threads use tactical mode

2 = every second thread uses tactical mode (50% of the threads will be in tactical mode)

4 = every fourth thread uses tactical mode (25% of the threads will be tactical)



When Tactical Mode is active, Houdini modifies its search process and uses some clever tricks to focus on tactical solutions in the root position. In Tactical Mode Houdini becomes a very skilled tactical problem solver.


Below some results for two popular tactical test suites with Houdini running at 20 seconds per position with 2 threads on a Core i7-5820K @ 3.9GHz using 512 MB hash.


Arasan 19 Tactical Suite, comprising 200 medium to hard positions

- Houdini 4 (normal mode) solves 123 positions, total solution time 34:59 minutes.

- Houdini 5 (normal mode) solves 124 positions, total solution time 35:30 minutes.

- Houdini 6 (normal mode) solves 154 positions, total solution time 25:34 minutes.


- Houdini 4 Tactical Mode solves 158 positions, total solution time 24:31 minutes.

- Houdini 5 Tactical Mode solves 168 positions, total solution time 20:57 minutes.

- Houdini 6 Tactical Mode solves 172 positions, total solution time 16:17 minutes.


Sedat test suite of 100 positions

- Houdini 3 (normal mode) solves 50 positions, total solution time 23:05 minutes.

- Houdini 4 (normal mode) solves 42 positions, total solution time 24:17 minutes.

- Houdini 5 (normal mode) solves 57 positions, total solution time 22:30 minutes.

- Houdini 6 (normal mode) solves 62 positions, total solution time 19:31 minutes.


- Houdini 3 Tactical Mode solves 72 positions, total solution time 15:47 minutes.

- Houdini 4 Tactical Mode solves 72 positions, total solution time 15:37 minutes.

- Houdini 5 Tactical Mode solves 74 positions, total solution time 14:21 minutes.

- Houdini 6 Tactical Mode solves 76 positions, total solution time 12:42 minutes.


Note that the focus on tactical moves will reduce the playing strength of the engine, the Tactical Mode is significantly weaker than the normal playing mode.

Using Tactical Mode value 2 (meaning that half the threads are tactical, assuming you're running at least 2 threads) will cost about 20 Elo.


One can compare the Tactical Mode to what a human player does when he/she tries to solve a test position in a chess magazine or website. He/she will scan for tactical, forcing moves, threats, sacrifices etc. That way a lot more tactical solutions can be found than what the player would actually see and decide to play over the board, during a normal game. The "this is a test position" message changes the search strategy.

Houdini's Tactical Mode works exactly the same, very human-like: it will spend a lot more time looking for tactical moves, threats etc. In most positions this doesn't provide any benefit - most of the time there is no tactical solution available and the increased focus on tactics is just wasted. But in test positions (selected because there IS a tactical solution) it works extremely well.



Limit strength from 0 (beginner) to 100 (full strength).

Default is 100 (full strength).


The strength reduction is mostly based on a combination of two techniques:

Limiting the number of positions searched - this reduces mostly the tactical strength of the engine;
Purposely picking a move the engine knows is not optimal - this reduces mostly the positional strength of the engine.

The combination of the two produces a game with both tactical and strategic (positional) flaws.


The following table shows the estimated Elo of Houdini at reduced Strength levels.


Strength   0 => 1000 Elo
Strength  10 => 1300 Elo
Strength  20 => 1600 Elo
Strength  30 => 1900 Elo
Strength  40 => 2200 Elo
Strength  50 => 2500 Elo
Strength 100 => 3200 Elo


This table is very approximate - we welcome any feedback from rated players that could improve these values.

What is the highest strength level that you can consistently beat?



UCI-protocol compliant version of Strength parameter.

Default 3200, min 1000, max 3200.


Internally the UCI_Elo value will be converted to a Strength value according to the table given above.

The UCI_Elo feature is controlled by the chess GUI, and usually doesn't appear in the configuration window.


UCI_LimitStrength (checkbox)

Activate the strength limit specified in the UCI_Elo parameter.

This feature is controlled by the chess GUI, and usually doesn't appear in the configuration window.



Number of principal variations shown.

Default 1, min 1, max 220.

The MultiPV feature is controlled by the chess GUI, and usually doesn't appear in the configuration window.



Limit the multi-PV analysis to moves within a range of the best move.

Default 0, min 0, max 999.

Values are in centipawn. Because of evaluation corrections in different stages of the game, this value is only approximate.

A value of 0 means that this parameter will not be taken into account.


Ponder (checkbox)

Have the engine think during its opponent's time.

The Ponder feature (sometimes called "Permanent Brain") is controlled by the chess GUI, and usually doesn't appear in the configuration window.



Level of contempt to avoid draws in game play.

Default 2, min -10, max 10.


The notion of "contempt" implies that Houdini will try to avoid draws by evaluating its own position slightly too optimistically. Houdini will value its own pieces higher than the opponent pieces and will only exchange them if there’s a clear positional advantage in doing so.

The Contempt level can be chosen between -10 and 10. A contempt value of 2 will typically reduce the draw rate in a match by about 4%. The impact on the evaluation (the "optimism" of the engine, if you like) will be about 10 centipawn for each level of contempt.

The objectively highest level of play is achieved without contempt, i.e. Contempt value 0.


By default a non-zero contempt is only used during game play, not during infinite analysis. If you enable the Analysis Contempt checkbox, Houdini will also take into account the contempt for infinite analysis. Because of the asymmetry in the evaluations (the evaluation changes when you switch sides), this is usually not recommended.


Analysis Contempt (checkbox)

Activate Contempt for position analysis.


It is usually not recommended to activate the contempt for analyzing positions.

When contempt is active for analysis, the score of the analysis will be optimistic (over-evaluated) for White if the Contempt value is positive, and optimistic for Black if the Contempt value is negative.



The number of moves after which the 50-move rule will kick in.

Default 50, min 5, max 50.


This setting defines the number of moves after which the 50-move rule will kick in - the default value is 50, i.e. the official 50-moves rule.

Setting this option in the range of 10 to 15 moves can be useful to analyse more correctly blockade or fortress positions:

- Closed positions in which no progress can be made without some sort of sacrifice (blockade);

- End games with a material advantage that is insufficient for winning (fortress).


By setting FiftyMoveDistance to 15, you're telling the engine that if it cannot make any progress in the next 15 moves, the game is a draw. It's a reasonably generic way to decide whether a material advantage can be converted or not.


UCI_Chess960 (checkbox)

Activate Fischer Random Chess a.k.a. Chess960 games.

The Chess960 feature is controlled by the chess GUI, and usually doesn't appear in the configuration window.


Move Overhead

Specifies the extra time needed for each move in milliseconds.

Default 0, min 0, max 5000.


The time management will take into account the move overhead in the time usage of the engine. This can be useful for "sudden death" games (without time increment) or when playing engine games in which the move transmission has a time lag.

For sudden death time controls with minimal lag a “Move Overhead” value of 30 is recommended. The best value depends on the lag in your connection with the chess server, if your connection is slow you should use a larger value.


UCI Log File

File name for saving a log of all the UCI communication of the engine.

Specify a full file name that resides in a writable directory. For example, create a writable “C:\temp” directory and then use the value “C:\temp\houdini.log”.

Don't use a value like “C:\Program Files\houdini.log” - the program will exit because it cannot write to that location (it’s a read-only directory!).


Hide Redundant Output (checkbox)

If enabled, this option will remove some of the redundant lines in the output of the engine.

These lines contain information about fail high and fail low situation of the engine, and statistics at the end of each search iteration.

If you feel that engine output is too busy, check this option.


Own Book (checkbox)

If enabled, Houdini will try to use the Polyglot opening book specified in the "Book File" parameter.


Book File

File name for Polyglot opening book (usually with ".bin" extension).

Polyglot is a commonly used format for opening books. Each position can have multiple moves; Houdini will pick a move according to the "Best Book Line" parameter.

The engine implements repetition checks to avoid playing moves that generate 3-fold repetitions; this is particularly useful for Cerebellum Polyglot books with multiple moves.


Best Book Line (checkbox)

When disabled (the default value) Houdini will randomly pick a move taking into account the weights of the various moves available in the opening book. Moves with a higher weight will have a higher probability of being chosen.

If enabled, Houdini will always use the best book move (the move with the highest weight) found in the opening book.