What is RuyDos?

RuyDos is an open-source UCI-compatible chess engine written in C++ by Álvaro Begué in collaboration with José Manuel Morán.

How do I get started?

First you need an UCI-compatible user interface, then download an executable from the downloads page.

If we didn't provide an executable for your platform, you can always get the repository and compile it yourself. The code is written with some attention to portability, so it should be quite easy to do. If you have any issues, contact us and we'll be happy to help.


We initially developed Ruy-López in the late 90s. Ruy-López was written in C and over the years grew quite slow and unmanageable.

In 2013 RuyDos was started from scratch in C++. It uses a lot of techniques that weren't known in the 90s, like magic bitboards and late move reductions. The name is the Spanish procounciation of "Ruy 2", meaning the second program in the Ruy-López saga. It is also a homophone of the Spanish word "ruidos", which means "noises".

The plan was to start with a fairly simple evaluation function, work hard on the search so very fast games wouldn't have lots of tactical problems, then develop the evaluation function carefully. As of version 1.0.19 the evaluation function is still quite simple (~300 lines of code plus square-piece tables), so we hope there is a lot of room for improvement there.

In 2016 we started our attempts at using automated differentiation and gradient descent to tune the parameters of the evaluation function. After some initial success RuyTune was released so others could also play around with this interesting technique. However, more recent attempts have not been fruitful. Further research is needed.

In April 2017 the quality of play improved a lot, after a combination of search and evaluation improvements. In June 2017 we decided to make RuyDos open source under the very permissive MIT license, and progress continues at a rapid pace since.

How well does RuyDos play?

We believe RuyDos running on a fast desktop CPU is about as good as the best human chess players, although with very different strengths and weaknesses. If you want a more specific answer, look us up in CCRL or other rating lists.


We'll be happy to hear from you at alvaro.begue@gmail.com .

Thanks for using RuyDos!