WhatIs is a locally-served documentation system that runs on your machine at http://127.0.0.1:5001/WhatIs, providing instant command reference, real-time server status, and comprehensive AI guidance for both you and Vex. Unlike traditional documentation that you read separately, WhatIs is actively used by Vex for real-time command lookups and error recovery. This section explains how to access WhatIs, what content each of the nine tabs provides, and how Vex uses it as a knowledge base for self-correction.