I believe that the key metrics for Yelp are probably its unique visitors, user engagement, and mobile device traffic. Unique visitors serve as an essential indicator of how far Yelp's platform extends. User engagement tracks how users interact with Yelp's app or website, encompassing actions like writing reviews, uploading photos, and the duration of their browsing sessions. This metric indicates Yelp's effectiveness in attracting and keeping active users. Finally, with more consumers using their mobile devices to access online services, the traffic Yelp receives from these devices is a critical metric.