This document discusses tools and techniques for optimizing Ruby performance. It begins by looking at common expensive tasks like database operations, network access, and inefficient algorithms. It then discusses tools for benchmarking and profiling Ruby code like Benchmark, benchmark-ips, and stackprof. The document provides examples of optimizing ActiveRecord queries and using caching and memoization. It also discusses optimizing the environment through server, database, and caching configuration. Finally, it notes that in some CPU-intensive or async tasks, Ruby may not be the best tool.