Guardrail Adapter
The guardrail adapter bridges API gateways to guardrail providers using Envoy’s External Processing (ext_proc) API. It intercepts MCP tool-call traffic in real time and applies content moderation, PII masking, or policy enforcement without modifying the agents or tool servers on either side.
The adapter is one provider implementation in the Agentic Layer guardrail story.
Platform teams typically deploy it automatically through the tool-gateway-agentgateway operator, which creates and wires a dedicated adapter instance for each Guard resource attached to a ToolGateway.
It can also be wired into a vanilla Envoy proxy independently of the operator layer.
For the broader guardrail architecture see Guardrails: Guard and GuardrailProvider.
Pages
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Deploy the Guardrail Adapter — deploy the adapter and connect it to a gateway
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Guardrail Adapter Reference — CLI flags, gRPC surface, HTTP endpoints, provider interface
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The Guardrail Adapter — design rationale, trade-offs, and how the adapter fits the Agentic Layer