Last modified by Jarik den Hartog on 2024/03/21 16:27 · GitHub


OpenSesame is opensource, Python based software used for building and running behavioral experiments. It features an easy to use graphical user interface for basic task building purposes. More advanced tasks are created by using scripting in Python. OpenSesame can be used in combination with physiology and eye tracking.

Availability, Support and Advice

OpenSesame is freely available. At the FSW Leiden it is preinstalled on all lab computers (see the Software List to check which version). For work computers it can be requested for at the ISSC Helpdesk. For unmanaged/personal computers, it can be downloaded here

SOLO provides full support for OpenSesame and recommends its usage to anyone who has some experience with Python, or is willing to learn. For highly timing critical tasks, E-Prime is recommended.

OpenSesame versions

OpenSesame version 4.0 was released recently. The lab computers at FSW Leiden will continue to run OpenSesame 3, until we can transition with minimal hindrance to ongoing studies. See the software list for a complete overview of software and their versions that are installed on the lab pc's.

 Some important notes when you are planning on doing research with OpenSesame:

  • OpenSesame 4 is not fully backwards compatible, this means that tasks created in OpenSesame 3 will likely not run without adjustments in OpenSesame 4. Similarly, tasks created in OpenSesame 4 do not run in OpenSesame 3. See for changes that were made the release notes of OpenSesame 4.
  • When you want to make use of the preinstalled OpenSesame version on the lab computers, make sure to build your task in OpenSesame 3 (current version installed on most lab pc’s is 3.14).
  • When you want to use OpenSesame 4 on a lab computer, you can use Anaconda to create a virtual environment in which you can run OpenSesame 4. See the OpenSesame download page for more information.
  • The information displayed on the OpenSesame website (e.g. manuals, tutorials, documentation), will now show the information relating to version 4 by default. Unfortunately, this information may sometimes differ from OpenSesame 3 in important ways. Therefore, always make sure you select the right version of the website to display (in the top menu-bar to the right of the "Support" button), i.e. v3.3. for the version of OpenSesame used in the labs.
  • Finally, for experiments that you plan to run (solely) online, we do recommend trying OpenSesame 4 on your own laptop/pc, as it also comes with a new version of OSWeb that has some nice new features

We do not know yet when OpenSesame will be updated on the lab computers, but we will keep the researchers informed. If you have any questions, please contact

OpenSesame on a Mac

Although SOLO does not support Mac, here is some info on installing OpenSesame on a Mac.

  • Go to the OpenSesame download page and follow the instructions.
  • Because an ICCS supported/maintained Mac does not seem to allow one to write to the Applications folder; copy/drag the OpenSesame application to your Desktop (for instance).
  • Control-click the OpenSesame application icon, then choose Open from the shortcut menu.
  • Click Open again and have some patience.

Online & OSWeb

OSWeb is an extension of OpenSesame, which allows for Javascript version of OpenSesame experiments to be run online (e.g. on JATOS or Pavlovia). For information about OSWeb, see our dedicated OSWeb page.


For information on using OpenSesame with Tobii eyetrackers, see here.


  • The OpenSesame website provides tutorials and manuals
  • Sebastiaan Mathôt made several Youtube video's about OpenSesame and Python, which can be found here


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