InternalBlue is a Bluetooth experimentation framework that enables security researchers to interact with Broadcom Bluetooth chip firmware at a low level. The framework was developed through reverse-engineering the firmware interaction and update mechanisms of Broadcom chips, providing researchers with capabilities to inject and monitor packets directly at the link layer. InternalBlue supports various research activities including protocol analysis, vulnerability research, and attack prototype development for Bluetooth communications. The tool allows researchers to bypass normal Bluetooth stack limitations and interact directly with the underlying firmware, enabling deeper analysis of Bluetooth security mechanisms and potential weaknesses. It provides functionality for packet injection, monitoring, and manipulation at the Bluetooth link layer, making it useful for understanding Bluetooth protocol behavior and developing security assessments.