Agents are only as safe as the tools you expose. Treat every function call as an external capability with explicit contracts, policies and isolation.
Start with a capability model. Enumerate allowed actions by domain (payments, content, tickets) and map them to personas and contexts. Only register tools that the current user and session are entitled to invoke; avoid global catalogs that agents can freely explore.
Define typed contracts for each tool: required inputs, allowed ranges, units, side-effects and audit fields. Reject invocations that are incomplete, ambiguous or risk-prone—do not rely on the model to self-correct. Prefer idempotent, reversible operations, and gate irreversible actions behind multi-step confirmations.
Add guardrails around tool execution. Use policy engines to validate parameters, rate-limit calls, enforce sequencing (e.g., verify identity before issuing refunds) and strip prompts of untrusted instructions. Run tools in sandboxes with scoped credentials and record every call with user, session and trace IDs.
Design the runtime for graceful failure. Provide safe fallbacks when a tool is unavailable, and surface compact error summaries back to the agent so it can decide to retry, escalate or stop. Simulate attacks such as prompt injection and payload tampering to harden before production.
Continuously observe behavior. Monitor tool mix, abnormal parameter patterns, success rates and downstream incidents. Feed those signals into refinement loops that tighten contracts, adjust capability exposure and retrain policies as usage grows.