This document describes ECL-Watch, a performance tuning tool for HPCC Systems. ECL-Watch allows users to analyze the performance of big data applications running on HPCC Systems. It provides fine-grained monitoring of application performance down to the function level to detect hotspots. ECL-Watch also monitors system performance and resources to identify bottlenecks. The document presents two case studies where ECL-Watch was used to optimize application and system performance, resulting in a 15% speedup of a K-Means clustering application. ECL-Watch provides essential performance tuning capabilities for both application programmers and system administrators working with HPCC Systems.