What is Agent Middleware?
Infrastructure sitting between an AI agent and external systems (MCP servers, APIs, databases), intercepting and processing requests before they reach their destination. Policy-enforcing middleware validates tool calls and applies governance rules transparently.
WHY IT MATTERS
The middleware pattern is proven: web application servers between clients and databases, API gateways between clients and services, reverse proxies between users and web servers. Agent middleware applies this pattern to AI agent tool calls.
MCP middleware intercepts tool call requests, evaluates them against policies, enriches them with context (logging, tracing), and forwards approved calls to the upstream server — or blocks unauthorised ones. The agent and server are unaware of the middleware's presence.
This creates a clean separation of concerns: the agent focuses on reasoning, the server provides capabilities, and the middleware handles governance. Each component does what it does best.
HOW POLICYLAYER USES THIS
PolicyLayer is MCP middleware — a transparent proxy that sits between the MCP client and server. It intercepts every tool call, evaluates it against YAML policies, and forwards approved calls to the server. No code changes to the agent or server. No framework-specific plugins. PolicyLayer handles policy enforcement, audit logging, and rate limiting at the protocol level.