Harness engineering is the practice of designing, building and optimizing the scaffolding (tools, memory, prompts, environment and control loop) that turns a model's raw capability into reliable, goal-directed action.

• The harness is everything around the model that converts capability into action.
• As frontier models converge, the harness becomes the main lever of differentiation.
• Tool design, context management and memory often matter more than model choice.
• Harnesses must be observable and evaluated — you cannot improve what you cannot measure.
• Harness engineering is to agents what platform engineering is to cloud applications.