We present the ELIOT Experiment Builder (ELIOT), an open-source experiment builder that specializes in the integration of external hardware units into standardized laboratory experiments. ELIOT allows for various study designs that are customizable using HTML, CSS, and JSON. As an application for modularized JavaScript, it ensures flexible, robust, and comprehensive integration as well as synchronization of external hardware, by building on popular software frameworks. Studies and hardware code are packaged so that they can be shared with and adapted by other researchers, facilitating replication and standardization between laboratories. This paper serves as a tutorial to ELIOT. Weprovide an overview of the functionality, define terminology within ELIOT and explain the software’s internal architecture. Central to data representation and collection in ELIOT are JSON objects. We therefore include a short introduction to JSON for behavioral researchers who are unfamiliar with the data format. The software code is provided under an open-source license and is available along with further documentation, ready-to-use installers, and support channels at https://github.com/eliot-org/eliot-experiment-builder.