Web performance is critical, especially for complex applications that rely on multiple contexts like windows, iframes, and worker threads. Microsoft is addressing this with the Delayed Message Timing API, aimed at improving message handling efficiency in web apps. Delays in message processing can severely impact user experience, making apps feel unresponsive. The new API helps identify the root causes of these delays with specific properties that track how long messages are queued and the number of tasks blocking their processing. Three main types of slowdowns occur when messages are exchanged: when the receiving context is busy, when the task queue is congested, and when serialization and deserialization processes add overhead. The API introduces properties such as `blockedDuration`, `taskCount`, and `scriptTaskCount` to help developers diagnose these issues. For instance, `blockedDuration` tells how long a message waited before being processed, while `taskCount` reveals how many tasks were in the queue at that time. The API supports various contexts, including windows, tabs, iframes, and workers. Developers can collect performance entries from both sender and receiver contexts for a comprehensive analysis. The article provides a code snippet showing how to implement the API, which includes observing "delayed-message" performance entries. This tool aims to enhance the debugging process, making it easier for developers to optimize their applications. Microsoft is encouraging feedback on the API proposal to refine its functionality based on real-world developer experiences.