Best Free Chess Engine 2021: Double Round Robin Tournament!


What is the best Free Chess Engine (that can run on a standard laptop CPU)? I wanted to find out!

Before I continue: Yes, I know there is a Computer Chess Rating List. Yes, I know about TCEC and CCC. But they are using supercomputers, so what the heck, why not test it for myself on my own crappy laptop?

I purchased Fritz 17 for its ability to pit chess engines against each other (Arena Chess GUI is a free alternative).

I scoured the internet for the strongest chess engines freely available for download (preference for those actively developed within the last decade or so). I found 24:

  • Arasan 22.3 (2021)
  • Berserk 4.5.1 (2021)
  • Booot 6.4 (2020)
  • Critter 1.6a (2012)
  • Defenchess 2.2 (2019)
  • Equinox 3.20 (2014)
  • Ethereal 13.00 (2021)
  • Fire 8.11 (2021)
  • Fizbo 2 (2017)
  • Gull 3 (2014)
  • Hannibal 1.7 (2016)
  • Houdini 1.5a (2010)
  • Igel 3.0.5 (2021)
  • Koivisto 6.0 (2021)
  • Komodo 12.1.1 (2018)
  • Laser 1.7 (2019)
  • Nemorino 6.00 (2021)
  • Nirvanachess 2.5 (2020)
  • Rofchade 2.3 (2020)
  • Rybka 2.3.2a (2007)
  • Stockfish 14 (2021)
  • Texel 1.07 (2017)
  • Wasp 4.5 (2021)
  • Xiphos 0.6 (2019)

I gave a 25th spot to Fritz 17 (2019), which is not free, but it since it hosted the tournament I threw it into the mix (useful as a benchmark). Wherever possible, I use the BMI2 version of the engines (the technical details elude me, but is seems these are the strongest versions if the CPU supports them).

Now, before you ask where is Lc0, let me specify that I ran this tournament on a CPU, not a GPU, so Lc0 and other neural network chess engines would be at a huge disadvantage (they run very very slow on CPUs). True, Stockfish and Ethereal now train with neural networks, but they still run at full speed on CPUs!

The tournament took place on Windows 10 x64 laptop with Intel Core i7-8750H (6 cores, 2.20 GHZ) and 8 GB RAM.

The tournament was a double round robin (each engine plays each other twice, once with each color). That is 600 games! Time format was 1 min + 1 sec increment. No opening books, endgame tablebases, or any tinkering. I just loaded the engines and let them play on their default settings. (Note: Fritz 17 seems to have a built-in adjudication feature for obvious results).

Results [to enlarge: right click, open in a new tab]:

Well, of course, Stockfish won easily. Actually, I am kind of surprised by the three draws, including one where Stockfish had white! Here are those games:





So, in conclusion, Stockfish still reigns supreme. As far as free CPU-based engines go, there seems little reason to consider anything else.


Thank you for taking the time to do this.


sry for being a couple months late, but can someone pls explain how the first match ended in a draw, if stockfish promotes to queen thats mate

kwality wrote:

sry for being a couple months late, but can someone pls explain how the first match ended in a draw, if stockfish promotes to queen thats mate

theres perpetual check with threefold repetition after bxc2+ before stockfish is able to promote

Stockfish is favored by “human” players on this site