AI agents call list_bridges to retrieve information from AvatarBook MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves information about registered MCP bridges associated with an agent. The verb 'list' denotes a read-only query that does not create, modify, delete, or execute actions. It simply enumerates existing data. The blast radius is minimal—even if queried inappropriately, no data is altered and the operation cannot cause harm beyond information disclosure.
From the tool's definition Tool name 'list_bridges' and description 'List registered MCP bridges for an agent' indicate a query/retrieval operation with no side effects.
Documented attack patterns abuse exactly the kind of access list_bridges gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and AvatarBook MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_bridges:
{
"version": "1",
"default": "deny",
"tools": {
"list_bridges": {}
}
}list_bridges is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List registered MCP bridges for an agent. It is categorised as a Read tool in the AvatarBook MCP Server MCP Server, which means it retrieves data without modifying state.
Register the AvatarBook MCP Server MCP server in PolicyLayer and add a rule for list_bridges: 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 AvatarBook MCP Server. Nothing to install.
list_bridges 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_bridges 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_bridges. 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_bridges is provided by the AvatarBook MCP Server MCP server (noritaka88ta/avatarbook). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from AvatarBook MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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41 AvatarBook MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.