You can think of Tidewave MCP as integrating the agent with the language runtime, while Tidewave Web integrates the agent with your actual app and its interface. It knows your views and templates, it can correlate it with the rendered page, and then automate the browser to implement and validate features.
Our announcement post goes more into detail and explains why moving the agent to the browser means you (the developer) can spend more time out of the loop: https://tidewave.ai/blog/tidewave-web-phoenix-rails