50 Shades of Stockfish

Sherwood, Russell  Tuesday, February 21, 2017

The Stockfish Chess Engine is undoubtedly one of the strongest available at the moment. Its ongoing open-source communal development continues to make it stronger. A side effect of this development is that a number of different versions, clones and copies exist some of which may be of interest to the aspiring correspondence chess player.

One word of caution, there are a number of rating lists which rate these versions; almost all have a common failing - the test games are run at very short time controls. You would not compare 10,000m runners by looking at their 100m times and the same is true here - be very wary of rating lists.


Stockfish 8

This is the "vanilla"  version of Stockfish, of the shelf with releases every 6-9 months. This is a solid place to start and all other versions should be compared to this.

Stockfish Development Versions

These are small improvements which are released every few days. Each ones undergoes rigerous self testing where the Develop version plays potentially tens of throusands of games against the current version - to have been released it needs to have shown statistically better results. Typically each improvement results in a tiny elo gain but when added together these become significant. Common opinion is that we should wait a week or two until after release as very occasionally new versions are rolled back.


Most of the Clones/Copies of Stockfish fall into two areas - either ones which try and increase its speed or ones which change either its evaluation or search functions.


This is a rewrite of  Stockish in Assembler, rather than the C++ Stockfish is coded in. (If this is gobbledygook to you dont worry!) The outcome of this is that AsmFish runs around 20-30% faster than Stockfish or Stockfish Development Versions. This does not mean that the engine searches 20-30% deeper but conducts the same search 20-30% faster which is very useful in analysis! Asmfish gives the same result a Stockfish in 99% of situations due to slight coding differences. For those who want a 100% congruence with Stockfish a Pedantfish version exists.


is a very similar idea to AsmFish, except the C language is utilised. What is interesting is that some users find CFish to be faster than AsmFish whilst others find AsmFish to be faster. Personally I have found the engines to work better in different positions.  A version called Goby has been coded for the Mac -although versions of this also work on Windows!

Different Compilations

A number of helpful people compile their own versions of Stockfish Development versions. These can be around 10% faster than the basic versions.

Stockfish BYO or Stockfish Rockwood

This is an utility which will complie a copy of the lastest Stockfish development versions on your machine. This means the engine should be optimised for your hardware and environment.


So moving onto versions which do more than speed up Stockfish.....



A very interesting project. The engine itself is a copy of the latest Development Build with one important modification: the addition of the Cerebellum opening book. This book is engine generated and fully consistent. How is this different from any other opening book? In a typical opening book we mat have a position that appears to be scoring 75% and have an engine evaluation of +0.9. A number of move later, due for example to transpositions this may now be 55% and the evaluation has dropped to +0.3. In the Cerebellum book the earlier position would have the +0.3 evaluation rather than the +0.9. At the moment the book is only utilised in Engine v Engine matches rather than analysis but the Full Cerebellum book is due to come available March 2017 at which point it will become a very interesting tool.


Stockfish is optimised for fast time controls. CorChess is an attempt to optimise it for slower time controls (such as those used in CC). In its earlier in its development but is already showing promising results.


A cross between Stockfish and the authors own engine. More options (including piece values) but does not appear to offer much to CC players.

Stockfish Matefinder

Think you may have a knockout move in a position? Then SF Matefinder may be for you. This version search for tactical killer moves and when used in right way can be devastating.


An offshoot which has been in on-off development for quite some time. Current direction is to develop certain Komodo style features.


An offshoot of CFish with a number of interesting options drawn from other engines. Worth examination.


A new kid on the block but with some interesting features including a study mode (giving a shallower but wider search)


A highly tactical version of Stockfish designed for fast time contols, where it perfoms much better than Stockfish.


A close cousin of Shark. Again more of a Fast Time control optimiser.


One of the first deviations from Stockfish. Interesting play but appears to have fallen behind in terms of playing strength.


A modified Stockfish which targets searching at greater depths. This of course comes at a cost - the potential to miss things!



Ive not mentioned a number of other variants: Don, Matrix, Ultron, Salt......as the list is almost endless. I would recommend that an aspiring player takes a look at all the engines listed but my advice is the either AsmFish or CFish, Matefinder and CorChess should be part of your stable of engines. Of course knowing how and when to utilise them is something or another day!

Why no links? These change often so Google is a better starting point.:

Updated Tuesday, February 21, 2017 by Russell Sherwood

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