Running web-based experiments is a great way for researchers to conduct studies without having participants necessarily be physically present in a lab. These web-based experiments run in the participant’s own web-browser—optionally full-screen—and can take the form of practically any type of computer-based task.

Gorilla, Pavlovia and JATOS are examples of platforms built to facilitate the execution of online studies. They provide a user-friendly interface and workflow for creating web-based experiments, hosting those experiments and the data they generate, and recruiting participants. Depending on the platform used, the web-based tasks can be built in the platform itself, or using standard experiment-building software; such as, OpenSesame, jsPsych, lab.js, and PsychoPy.

For a full overview of software built for online studies and the issues associated with them, please refer to this article.

JATOS (Just Another Tool for Online Studies) is a platform for hosting online studies. It takes care of making the study available online, storing the data it generates, and managing the users. Experiments for JATOS can be built using third-party packages, such as OpenSesame, lab.js, or jsPsych; or with HTML, CSS and JavaScript.

SOLO makes a JATOS instance available at no cost to researchers, and can offer limited technical support in building and running JATOS studies, as well as post-processing the data it generates. For more information, see the SOLO JATOS server page.

Gorilla is an easy-to-use platform for both hosting and building online studies. It offers: a fully graphical experiment-builder; powerful scripting; tools for creating questionnaire and surveys; a large collection of examples; and great documentation, including video tutorials.

SOLO has a department account for Gorilla and can provide FSW researchers with tokens. Please enquire via:

Pavlovia is a platform for hosting, sharing and running online studies. It does not feature a built-in experiment-builder, but experiments can be created in PsychoPy, lab.js or jsPsych and uploaded to it.

SOLO currently has an unlimited-usage site-license for Pavlovia, and any accounts registered to,, and will automatically be granted access to the subscription. For more information, please mail:

JATOS, Pavlovia and Gorilla have both overlapping features and unique use-cases. This section presents a concise outline of the main reasons to use a particular platform.

Use JATOS when:

  • You have experience with OpenSesame and want to use it to build your experiment, or you have a pre-built OpenSesame experiment you want to convert for online use.
  • You have an existing experiment built in HTML, CSS, and JavaScript that you want to host online (this includes jsPsych or lab.js tasks).
  • You want to program your task from scratch in HTML, CSS and JavaScript; or using a JavaScript library, such as jsPsych or lab.js.
  • You want to build multi-participant interactive tasks, such as a prisoner's dilemma game.
  • GDPR considerations require you to store the data you collect internally; i.e. on a server owned and managed by the Leiden University.

Use Pavlovia when:

  • You have experience with PsychoPy and want to use it to build your experiment.
  • Your task requires scripting, and you necessarily want to use Python instead of JavaScript.
  • You can make do without technical support from SOLO.

Use Gorilla when:

  • You have experience with Gorilla or have found a preexisting Gorilla experiment that you want to run; or modify and run.
  • You want a super easy-to-use platform with integrated experiment-building and survey/questionnaire tools.
  • You are fine with your experiment being forever locked-in to the Gorilla platform; experiments built in Gorilla cannot be exported and run without a Gorilla license.
  • You do NOT intent to collect data from a large number of participants (»500). This is due to Gorilla being a pay-per-participant service, unlike JATOS (free) and Pavlovia (flat fee).

Don't run web-based experiments when:

  • Your experiment needs to connect to hardware (e.g. when recording physiological data).
  • You require millisecond accuracy.

Note: when creating experiments for online studies that you intend to convert for use in a physiology lab, SOLO suggests using OpenSesame.

If you have any questions about online studies, please mail SOLO lab support at: To request advise regarding GDPR matters, contact

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