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z-Tree unleashed

C-SEB researchers at the Cologne Laboratory for Economic Research have developed a new tool for conducting online experiments based on the established z-Tree software. z-Tree unleashed allows subjects to participate in z-Tree experiments via web browser. The administration of the experiment is also possible using a web browser. “For the first time, it is now possible to play z-Tree experiments over the internet without malfunctions or interruptions,” said Max Grossmann, CLER laboratory manager and lead developer. “Everything is completely platform-independent, all you need is a browser.” The associated paper is Duch, M. L., Grossmann, M. R. P., & Lauer, T. (2020). z-Tree unleashed: A novel client-integrating architecture for conducting z-Tree experiments over the Internet. Journal of Behavioral and Experimental Finance, 28, 100400. Further information is available on the z-Tree unleashed website or from the developers at


zTree unleashed Add-Ons

zTu - Preleaf

This useful Add-On shows which Participants are actively participating. So participants will only be shown in the clients table if they are active. You can easily screen inactive participants and exclude them from the experiment. Here you find further information.

zTu - Singlelink

With this tool you are able to send out only one link to your participants. The participants will be redirected to a personal link. With this you can save time by not sending every participant a personal link. Here you will find further information.


Further CLER Tools

CLER Collector

This tool separates the results of the experiment and the payment data. With this you can carry out the payment without having to look into the results of the experiment. Especially for data protection purposes this tool offers a lot of benefits and makes the payment a lot easier. Here you will find further information.

CLER Communicator

With this tool for zTree you are able to communicate with the participants during the experiment. The communication is possible by using a chat window on the upper edge of the screen. Every participant can be texted separately, and the communication will be saved within the results of the experiment. Here you will find further information.


For the first time in experimental history, AnonPay made it possible to safely collect payment details within the experiment. With AnonPay you can directly collect payment information within zTree and oTree. The payment information are anonymised instantly. With this AnonPay helps to enhance privacy in online experiments. Here you find further information.