Embedded Client Side Paradata (ECSP) is a tool that is licensed under the Creative Commons Attribution 4.0 International License (see http://creativecommons.org/licenses/by/4.0/). It is based on different program languages, such as JavaScript and HTML. In general, ECSP can be implemented in web-based survey software solutions that provide access to the source code. It enables researchers to passively collect different kinds of client-side paradata, such as response times and scrolling events – irrespective of the Internet browser and operating system used – to investigate respondents’ completion behavior with respect to web surveys. Paradata are collected at the page-level and are stored together with the actual survey data (i.e., respondents’ answers) in the same dataset.