Tool Contract

A tool contract is the explicit agreement between an AI agent and a tool it is allowed to call. It defines far more than a function name. A useful contract covers input fields, data types, allowed values, permissions, side effects, error cases, time limits, return shape, and the situations in which the agent should use the tool at all. Without that contract, the model has to infer behavior from a loose description, which often leads to invalid parameters, unnecessary calls, or risky actions. A good tool contract makes the boundary between reasoning and acting testable. It states which data the agent may pass, whether a call is read-only or mutating, how sensitive information is masked, and when human approval is required. In production agent systems, the tool contract is therefore a safety and quality primitive, not just documentation. It connects the prompt, API schema, access control, and tests into a clear interface that both the model and engineers can rely on.