Modern enterprises are saturated with telemetry. Endpoint agents, centralized logging, behavioral analytics, and automated detections have made off-the-shelf red team tools increasingly brittle and predictable. Most red team tools fail not because they're buggy, but because they behave in ways detection systems are designed to notice. Red Team Tool Development teaches readers how to think, design, and build differently. Instead of showing how to run popular frameworks, this book focuses on how offensive tools actually behave in monitored environments and why that behavior so often gives them away. The authors walk readers through the foundations of detection-aware tool design, explaining how payload structure, execution flow, and environmental interaction influence visibility across modern detection stacks. Each chapter centers on modular, adaptable examples that show not just what works, but why it works. Readers learn how small design decisions surface in logs, alerts, and behavioral analytics, and how thoughtful toolcraft can reduce detection while still achieving realistic adversary objectives. The result is a field-ready reference for red teamers who need to build their own tools when public ones fail, and for detection engineers and threat hunters who want a clearer view of how advanced operators design tooling to evade automated defenses.