DeepSeek Harness is a versatile open-source framework crafted to ensure that AI agents can effectively operate in dynamic real-world situations by enhancing their understanding of context, tool utilization, and the ability to manage intricate tasks. Utilizing the Cordis plugin architecture, it allows for the selection, modification, and reconfiguration of various capabilities without necessitating any alterations to the underlying source code. Each plugin contributes essential features, such as models, tools, skills, and session management, while Cordis oversees the integration of plugins, along with their dependencies, services, and event handling. A comprehensive session log, which is append-only, captures each run's details, documenting system prompts, reasoning processes, tool interactions, results, scheduling of subagents, and context adjustments. Developers can analyze these logs through the Trajectory view, which organizes records by their source, and they have the ability to utilize functions like resume, fork, search, and replay that interact seamlessly with the same event stream. This structured approach not only aids in troubleshooting but also enhances the overall efficiency of AI development and deployment.