Webhooks are essential for receiving notifications about specific events, such as email openings or calendar deletions, and can be tested locally using the Nylas Java SDK, sparing the complexity of web server testing. Local testing is advantageous because it allows quick fixes without the need to repeat extensive workflows, ensuring everything functions correctly before deployment. The guide details the creation of a SparkJava application with Twilio integration to send SMS alerts for events like email link openings, gathering comprehensive information about each event, including sender and recipient details and the webhook type. It involves setting up a Twilio account, creating a Java Webhooks project, and compiling and running the application locally on a designated port. This local testing approach is promoted as a time-saving measure that prevents errors, with further resources available for those interested in expanding their knowledge of webhooks.