We introduce WaRR, a tool that records and replays with high ﬁdelity the interaction between users and modern web applications. WaRR consists of two independent components: the WaRR Recorder and the WaRR Replayer. The WaRR Recorder is embedded in a web browser, thus having access to user actions, and provides a complete interaction trace—this confers high recording ﬁdelity. The WaRR Replayer uses an enhanced, developer-speciﬁc web browser that enables realistic simulation of user interaction—this confers high replaying ﬁdelity. We describe two usage scenarios for WaRR that help developers improve the dependability of web applications: testing web applications against realistic human errors and generating user experience reports. WaRR helped us discover bugs in widely-used web applications, such as Google Sites, and offers higher recording ﬁdelity compared to current tools.