Introduction

JATOS (Just Another Tool for Online Studies) is a platform that allows researchers to manage, distribute and run studies online using their own servers. Participants can access these studies via the internet on any device with a browser; and researchers can login to JATOS to upload, customize and manage studies, and export their data. Study components can be built manually with HTML, CSS and JavaScript; or using third-party packages, such as OSWeb, lab.js, or jsPsych. JATOS can also be interfaced with Prolific, SONA and Qualtrics.

SOLO makes a JATOS server available at no cost to FSW researchers.

General Information

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Support and Advice

SOLO can offer technical support in building and running JATOS studies, as well as post-processing the data it generates. For researchers with limited programming experience, SOLO recommends building JATOS compatible tasks in OpenSesame/OSWeb. However, for researchers with JavaScript experience seeking to build complicated tasks, jsPsych provides a much more flexible solution.

If you have any questions regarding JATOS, please email labsupport@fsw.leidenuniv.nl.

SOLO JATOS Server

The SOLO JATOS server is available at no cost to FSW researchers (and for now to all Leiden University researchers in general), and can be reached via: jatos.services.universiteitleiden.nl

Requesting Access

 As of September 2025 all students and staff members can make an access accounts on JATOS using the SurfConext login option and logging in with their regular ULCN details. Local and shared accounts are no longer supported.

JATOS Usage Guidelines

When using the SOLO JATOS server, the following rules must be observed:

• JATOS accounts are strictly personal.
• Please indicate if an account is no longer active and can be removed.

Accessing the JATOS GUI

For security reasons, the JATOS GUI can only be accessed from within the Leiden University intranet. Studies, however, can be run by anyone with access to the internet. Attempting to navigate to jatos.services.universiteitleiden.nl from outside the university network will result in a 403 Bad Gateway error.

To access the JATOS GUI, navigate to the server using:

• a browser on any PC connected to EduVPN.
• a browser on any ISSC-issued PC or laptop connected to the university network (not eduroam).
• a browser on your own university PC, accessed via Remote Desktop Protocol (RDP).

EduVPN

The JATOS GUI is accessible from a PC connected to EduVPN (with the Leiden University profile).

University PC

Any desktop or laptop connected to a wired or wireless Leiden University network should be able to reach the JATOS GUI (jatos.services.universiteitleiden.nl). Eduroam, however, does not provide access to the JATOS GUI, unless used in conjunction with EduVPN.

RDP

University staff can remotely gain control of their own personal work PCs using the Remote Desktop Protocol (RDP). Through RDP, the JATOS GUI can be accessed normally. For more information about RDP, please visit refer to the ISSC Helpdesk. Note that the RDP service is subject to approval by the ISSC and may not be available to everyone.

Creating a Study from Scratch

To create a study, that is a jzip file from an html file and assets:

• First, install a local JATOS server, see Local JATOS Server.
• Follow the instructions here: Create a new study | JATOS, chapter Write your own study from scratch, then follow the instructions here: Write your own study - Basics and beyond | JATOS. It is important to add all relevant study assets to the study assets folder!
• Try running the study.
• When it runs as expected, Export the study to jzip.

Cloning a Study

Cloning a study may be necessary when you try to upload a study that already exists on the JATOS server that you are using. To be able to upload the study, you will need to clone the study in your local JATOS instance. This will generate a new study with a new UUID (Universally Unique Identifier), which you can then upload to the JATOS server.

These steps are necessary when you get the following error in JATOS when trying to import a study: "Import of study failed: The study you're trying to upload already exists but you aren't a user of it..."

• First, install a local JATOS server, see Local JATOS Server.
• Go to My Studies and Import Study.
• Import the jzip file.
• Go to the button More and hit Clone.
• The study is now cloned and you will see a new study appear on the left.
• Export this new study and try uploading it again on the JATOS server.

GDPR and Data Security

All studies conducted using the JATOS server must comply with the relevant regulations and guidelines; including, but not limited to, those regarding GDPR, Informed Consent, etc. In addition, all studies must be officially approved by the concerning authorities—ethical, medical and/or otherwise—before going public. Questions regarding these matters can be sent to privacy@fsw.leidenuniv.nl.

The JATOS server is maintained by the ISSC, and is physically located in The Netherlands. The data are backed-up regularly in an encrypted fashion, and all data are stored in compliance with the security regulations of Leiden University. Both participants and users communicate with the JATOS server exclusively through a secure internet connection (https).

Within JATOS, users only have access to studies that they have explicitly been made are members of. After a study has finished, and SOLO has confirmed that the data have been downloaded and secured, the study and all its data will be removed from the server. Accounts of users that are then no longer members of any other studies will also be removed.

SOLO and the ISSC will perform updates and/or maintenance to JATOS and/or its dependencies when they see fit, especially with regards to security patches. Users will be informed beforehand about possible downtime, and about expected consequences for ongoing studies.

Typical OpenSesame/OSWeb Workflow

OpenSesame is a free and open-source program for developing interactive experiments, and is already in use by various researchers at the FSW. Its latest version includes the OSWeb plug-in, which allows its experiments to be exported for use with JATOS—albeit with some important caveats. OSWeb does not support all OpenSesame features, and the customary Python-based in-line scripts must be replaced with their JavaScript-based counterparts. Please see the OSWeb documentation for more information.

The full OpenSesame to JATOS workflow is explained in great detail in this YouTube playlist. Additionally, the OpenSesame website features a very active forum where enquiries about OSWeb and OpenSesame itself can be posted and browsed through.

The following is a standard workflow for developing and deploying a study on the SOLO JATOS server:

1. Contact SOLO Lab-support:
   • It is recommended that you contact SOLO lab-support (labsupport@fsw.leidenuniv.nl) as soon as possible to announce your intention to use the JATOS server and describe your plans. This way, lab-support can provide you with relevant advice and access to the server.
2. Build OpenSesame experiment:
   • Familiarize yourself with OpenSesame and its OSWeb-plugin. Then build your experiment and test it out in your own browser using the OSWeb test feature.
3. Test experiment on local JATOS server:
   • Download and install a local JATOS test server, as described here. Read all relevant JATOS documentation, export the OpenSesame experiment for use in JATOS and upload it to your local JATOS server. Test the experiment thoroughly, and pay extra attention to the integrity of the data-saving process and the manner in which you wish to distribute your study once public. Once all functionality has been validated, export your study from the local JATOS server.
4. Upload the experiment to the SOLO JATOS server:
   • Upload the study you exported from your local JATOS server to the SOLO JATOS server using the account you received from lab-support.
5. Run the study:
   • Once the study is online, double-check everything, and distribute it when ready.
6. Finishing up:
   • Once data collection has been completed, and the data downloaded and secured, remove the study from the server. When user accounts are no longer needed, please delete them.

Uploading to JATOS with OpenSesame 4

If you are working with OpenSesame 4, you can upload your study directly from OpenSesame to JATOS, without having to export it as a jzip file.

1.  First, create your own API Token in JATOS (see here  for instructions).
2. In your experiment file in OpenSesame, go to Tools - OSWeb and JATOS Control Panel to connect your experiment to JATOS.
3. In the JATOS server field, change the server to https://jatos.services.universiteitleiden.nl. In the next field JATOS API token, enter the API Token you previously created in JATOS.
4. Then, just click on Save and publish to JATOS to upload your study. If you later discover that something in your experiment does not work as intended, you can just edit the experiment directly in the same OpenSesame file and click on Save and publish to JATOS again once you are done. 

JATOS Data

If you have OSWeb data, you can export the results as Plain Text, then open OpenSesame and go to Tools > OSWeb and JATOS control panel > and click Convert OSWeb results to .csv/.xlsx. Open the file you just exported from JATOS. Now, the data can be easily viewed in Excel. 

If you have other data, please see Problem with JATOS result conversion — Forum for more information.

Linking To and From Jatos

Worker Links

To link to Jatos experiments, you first need to make Worker links. There are multiple types of links possible, usually the most convenient is the general multiple worker. Please see these two pages for more info:

• https://www.jatos.org/Run-your-Study-with-Study-Links.html
• https://www.jatos.org/Worker-Types.html

To redirect from Jatos to a different website (e.g. SONA or Qualtrics), you can use the redirect feature:

• https://www.jatos.org/End-page-after-your-study-finished.html

Query Parameters

You can use query parameters both in the link to Jatos (e.g. from SONA) and in the redirect from Jatos, e.g. to pass on participant id.

SURFconext Migration

If you still have a local account, please make sure to migrate to a SurfConext account as soon as possible, see attached instructions

Local JATOS Server

For reading how to install the local JATOS server and usage of the local JATOS server, please refer to the official JATOS documentation. The local installation should be used for testing the tasks and exporting them to a .jzip file that can be used on the SOLO server.

Local JATOS Server on Windows 11

In Windows 11, there is a chance the loader.bat file does not work. This is due to the removal of wmic, and the change to the Java option flags. As a result, when running the loader.bat file, the command prompt is opened and immediately closes, and the local Jatos server does not run. 

To fix this, the loader.bat file needs to be edited (right-click > Edit). Note: it is possible that windows prevents you from opening the file because it doesn't recognize the app. A pop-up window will appear that says "Windows protected your PC". You will have to unblock the file as described here .

When you are able to edit the file, make the following changes:

• Remove the '--illegal-access=permit' flag on the line where it appears (see line here). This should produce the following line:

• If the problem remains, remove the call to the legacy wmic functionality. This is done by deleting the whole wmic block, as denoted here.

FAQ

JATOS Showcase

Examples showing the various JATOS features (taken from the JATOS site):

• Simple lexical decision task (full screen).
• Drawing and upload demo.
• Multiplayer snake game.
• 2048 game.
• Perceptual metacognition.