AI agents call list_agents to retrieve information from MCP-A2A-Gateway without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool performs agent discovery/enumeration through a read-only query. It retrieves information about registered agents on the A2A gateway but does not create, modify, delete, or execute operations. The blast radius is low—enumeration of agents poses minimal risk compared to registration, messaging, or task execution.
From the tool's definition Tool name 'list_agents' indicates a retrieval operation that queries available agents without modification. The verb 'list' is a standard read operation. No description provided, but naming convention strongly suggests data retrieval.
Documented attack patterns abuse exactly the kind of access list_agents gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP-A2A-Gateway, and nothing reaches the server without passing your rules. This is the rule we recommend for list_agents:
{
"version": "1",
"default": "deny",
"tools": {
"list_agents": {}
}
}list_agents is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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list_agents. It is categorised as a Read tool in the MCP-A2A-Gateway MCP Server, which means it retrieves data without modifying state.
Register the MCP-A2A-Gateway MCP server in PolicyLayer and add a rule for list_agents: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches MCP-A2A-Gateway. Nothing to install.
list_agents is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the list_agents rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for list_agents. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
list_agents is provided by the MCP-A2A-Gateway MCP server (yw0nam/mcp_a2a_gateway). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from MCP-A2A-Gateway, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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6 MCP-A2A-Gateway tools catalogued and risk-classified — across an index of 43,000+ MCP servers.