An agent harness is the software infrastructure that wraps around an AI model to manage its lifecycle, context, and interactions with the outside world. It is not the "brain" that does the thinking; instead, it is the environment that provides the brain with the tools, memories, and safety limits it needs to function. While an agent framework provides the libraries to build an agent, the harness is the actual runtime system that governs how that agent behaves in a real-world setting.
The quality of an agent often depends not only on the underlying model’s intelligence, but also on how well the surrounding system supports that model with context. In a production environment, an agent might encounter API timeouts, reach the limits of its memory, call tools out of sequence, or generate a reference to a non-existent API function that does not exist. Without a supporting structure, these errors lead to failure.
https://www.salesforce.com/agentforce/ai-agents/agent-harness/