FoundationHazelJS
Guardrail
Preventive or detective control enforcing safety, policy, or quality constraints on agent behavior.
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Direct answer
Preventive or detective control enforcing safety, policy, or quality constraints on agent behavior.
Plain language
Rails that keep the agent on the path—filters, allow-lists, validators, and blockers.
Technical explanation
Includes schema validation, ToolRegistry allow/deny, PolicyEngine, PII redaction, content filters, RunBudget enforcers, and approval requirements—preferably in runtime code via @hazeljs/guardrails + agent policy.
Example
Block outbound tool URLs not on an allow-list using guardrails before ToolExecutor egress.