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congame is the best experimental economics software written in Racket. zTree and oTree are two common experimental economics platforms. The reason for building congame is the usual: I used oTree for some of my experiments, but found that it lacked some specific features I needed in my experiments:

  1. It is tedious and errorprone to have multi-part studies across several days or weeks
  2. It is tedious and errorprone to reuse and compose substudies into larger studies
  3. Specification of the experimental study are interweaved with code that deals with web specific concerns

congame addresses the first concern fully, and eases the other two -- at least for the kinds of studies I run. Unsurprisingly, congame lacks many features of oTree (and other behavioral research software):

  • There is no easy way for studies requiring multiple participants to interact with each other or respond to each other
  • There are almost no templates for many existing tasks and designs

Furthermore, congame has a few features that many will consider bugs:

  • It is written in Racket
  • It is build on top of the koyo web development kit developed by the indefatiguable (except for lack of coffee) Bogdan Popa
  • There is precisely zero documentation (beyond the code itself)

koyo is much less battle tested than Django, the Python framework on which oTree is built, and Racket is a very uncommon choice compared to Python. This means that at this stage, it is fairly unlikely that you will want to use congame.

Future Vision

The vision is to develop congame further, in particular as follows:

  • Provide easy ways to implement strategic interaction between participants, such as prisoner's dilemma etc
  • Ensure easy ways to change and test treatments and randomization in the study in a way that is entirely independent from the web aspects of the studies
  • Allow for bots, in addition to users, to participate. This will benefit with simulations, debugging, etc - similar to mTree

The features that will get implemented will however be determined by the priorities of the studies that I am actually running -- hence strategic interactions may never be implemented, since my studies don't require that.



  • You need Racket since this is a Racket application.
  • You need node and nvm to build the assets.
  • You need access to a couple local Postgres databases. One named congame and the other congame_tests. The latter is exercised by unit tests.

First-time Setup

$ nvm use && npm install && npm run build
$ raco pkg install chief              # install and build chief to launch web server
$ raco pkg install congame-core/      # install and build the core library and its deps
$ raco pkg install congame-identity/  # install and build the application and its deps
$ raco pkg install congame-smtp-proxy # install and build the smtp-proxy dispatching traffic 
                                      # to the right identity server (staging or production)
$ raco pkg install congame-web/       # install and build the application and its deps
$ raco pkg install congame-doc/       # install and build the docs and their deps
# To install a package or study that tests depend on (e.g. congame-pjb-studies),
# uncomment the following line and replace by appropriate package.
# raco pkg install congame-price-lists/  # needed by congame-pjb-studies
# raco pkg install congame-pjb-studies/
$ raco pkg install congame-tests/  # install and build the tests and their deps

Development environment

Copy .env.default to .env. chief will automatically load the variables defined in this file into the environment of the subprocesses defined in the Procfile whenever it is run.

The app expects to be run behind an SSL terminated connection (for example, behind an nginx instance using a self-signed cert), even for local development . You can disable this requirement by setting current-continuation-key-cookie-secure? parameter to #f before the application is started.

Installing study packages

  • The package's info.rkt needs to (define congame-studies) like so:
(define congame-studies
  ;; Path to package, followed by the study provided by the package that you want to use
  '((congame-example-study/example consent-study)
    (congame-example-study/example simple-study)))
$ raco pkg install congame-example-study/  # install and build the study package and its deps

To get congame to pick up the new package, run

rm -r congame-web/studies/compiled/


touch congame-web/studies/all.rkt

This will cause the "all.rkt" module to be re-compiled, and that will in turn make the new study available in the web app.

Updating study caches

Run ./bin/ after adding studies or bots to info.rkt files within study packages.

Running the app locally

$ nvm use
$ raco chief start

Re-building the documentation

$ raco setup --tidy --check-pkg-deps --unused-pkg-deps congame

Deployment Recommendation

See ci/


The creation of this software was supported by Central European University (CEU).


congame is licensed under the 3-Clause BSD license.



The best experimental economics software built in Racket






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