The Web of Things (WoT) connects physical devices to the web using standard protocols. However, uncertainty in WoT service compositions may lead to critical problems in real- world applications. For example, in a smart hotel system, a user wishing to control the room temperature based on data from multiple sensors may get incorrect service compositions when using inaccurate or incomplete data, which can be dangerous in safety-critical situations. To address this issue, we propose a probabilistic approach that represents uncertain WoT services using Thing Description (TD) by including Quality of Thing (QoT) properties, interactions, and behaviors. Our approach computes the uncertainty of each node used in the composition process and proposes, using a WoT probabilistic algebra, an HTTP GET method that takes into account uncertain input and calculates the confidence degree of outputs when invoking WoT services. Our approach can improve the reliability of WoT services in uncertain environments and can be applied in various domains to create more robust and safer applications.