The Model Context Protocol is an open standard that lets an AI agent discover and invoke external tools — databases, APIs, file systems, internal services — through a uniform interface, rather than through bespoke integration code written for each one. An MCP server exposes a set of tools; an MCP client, typically an agent runtime, calls them. The protocol standardises how the tools are described and how the calls and responses are framed.
The governance consequence is the part enterprises miss. Every MCP tool invocation is two things at once: a data flow and a permission decision. The agent is reaching something that holds real data, and something decided it was allowed to. In most deployments nothing records either. The tool list an agent can reach is effectively an access-control surface that no one has inventoried, and it changes whenever a developer adds a server.
How it differs from an API integration. A traditional integration is written, reviewed and deployed by a person, and its permissions are fixed at build time. MCP is discovered at runtime: the agent asks what tools exist and decides which to call. That moves the authorization question from the build to the moment of execution — which is why MCP governance belongs in the runtime plane rather than in the workflow that assembled the agent.
How it differs from A2A. MCP governs an agent calling a tool. A2A governs an agent talking to another agent. The two often appear in the same architecture and need different controls.
APERION Shield is an open-source guardrail layer for MCP tool calls.
Governing MCP traffic
MCP turns tools into an addressable surface, and a surface any agent can call is a path into whatever that tool can reach. The governance questions are narrower than they first appear: which agents may reach which servers, which individual tools on a server are enabled, what credential the call carries, and whether a call that skips the governed path fails rather than succeeds. That last one decides whether the control is a policy or a suggestion.
A gateway in front of MCP traffic answers all four in one place, which is the approach documented in agentic governance and the AI agent governance guide. APERION Shield covers the local runtime case where the agent and the server sit on the same machine. Agent-to-agent traffic raises the harder version of the same question — see A2A and agent governance. How other gateways approach MCP is set out on the Kong AI Gateway comparison.
Related terms
A2A (agent-to-agent protocol) · Prompt injection · Policy as code · Agent authority scope · MCP security · Full glossary
Put this in the path of your own agents.
Policy enforced inline between your agents and every model and tool they reach, with a record bound to the human who owns it.
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