Build a Voice Agent That Won't Go Off Script

An effective AI agent, such as a hotel receptionist, requires multiple layers of defense to remain on track and handle various conversational scenarios, including adversarial inputs and off-topic requests. Starting with a structured prompt that clearly defines the agent's identity and boundaries, the system can guide interactions by detailing what the agent can and cannot do, thereby setting up "topical rails." Explicit instructions help protect against prompt injection attacks by instructing the agent not to deviate from its role, while specific code-level rules enforce constraints and validate inputs to prevent errors. The system is further strengthened by decomposing tasks into focused units with limited tools, ensuring the agent does not drift off-task, and by using a shared Userdata object to track the user's state and prevent redundant actions. Sensitive actions are gated behind verification tasks, and an independent moderation layer functions as an external check, ensuring that any prompt injection or error is corrected without interrupting the conversation. Continuous validation and testing, both offline and online, help catch any issues that slip through, with LLM judges and scenario-based tests providing additional safeguards. These layered defenses work together to maintain the agent's focus and reliability, even in challenging interactions.

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