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What is an MCP gateway?

An MCP gateway is a service that sits between AI agents and MCP tool servers. Agents call the gateway, and it forwards each exchange to the right server. A security gateway also inspects what passes and can refuse it.

How it works

Without a gateway, every agent connects to every MCP server directly. With a gateway, agents connect to one address, and the gateway holds one route per registered server:

agent → gateway /mcp/git      → Git MCP server
agent → gateway /mcp/tickets  → ticketing MCP server
agent → gateway /mcp/db       → database MCP server

When an agent lists tools, calls a tool or receives a response, the exchange passes through the gateway. A routing gateway simply forwards it. A security gateway reads it first: the tool list for poisoned descriptions, the call for secrets in its arguments, the response for planted instructions. When a call breaks policy, the gateway refuses it and the tool server never receives it.

MCP exchanges are JSON-RPC messages, defined in the Model Context Protocol specification.

Why classic controls miss it

  • An API gateway authenticates the caller, applies rate limits and routes requests. It does not read what a tool description tells the model.
  • MCP messages travel inside ordinary HTTP, often streamed. A gateway that checks headers and paths sees one valid request.
  • The risk lives in the content: an instruction in a description, a key in an argument, text in a response.
  • Without one central point, each team wires each agent to its servers separately, and nobody sees the whole boundary.

How to detect and prevent it

  1. Inventory every MCP server your agents connect to, and who approved each one.
  2. Route all agent-to-server traffic through one gateway, and block direct connections from agent hosts to tool servers.
  3. Register each server with its own route and its own policy.
  4. Log every tool list, call and response at the gateway, so you can say what an agent sent and to whom.
  5. Decide per threat class what to refuse and what only to record, then review the records each week.

How Cyron handles it

Cyron AI Security can run as a gateway in front of your MCP and A2A servers. Agents reach each server through Cyron, which inspects every exchange with 15 agent-layer detectors and refuses a malicious call before the tool is reached. Inside Cyron On-Premise it works from the kernel sensor instead, so agents are not re-routed. See Cyron AI Security.