Retrieve hosts from Mackerel. 🔍 USE THIS TOOL WHEN USERS: - Get a list of hosts - Filter hosts by various criteria (service, role, name, etc.) - Check host status and information <examples> Get all hosts (first 20) \
AI agents call list_hosts to retrieve information from Mackerel MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool only retrieves or lists data from the Mackerel monitoring platform with no side effects. It queries host information and applies filters, which is characteristic of a Read operation. The severity is low as it merely exposes existing monitoring data without capability to modify infrastructure, execute commands, or cause financial impact.
From the tool's definition Tool name is 'list_hosts' and description states 'Retrieve hosts from Mackerel.' The usage examples show filtering and checking host status/information without any modification, deletion, or external execution.
Documented attack patterns abuse exactly the kind of access list_hosts gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mackerel MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_hosts:
{
"version": "1",
"default": "deny",
"tools": {
"list_hosts": {}
}
}list_hosts is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Retrieve hosts from Mackerel. 🔍 USE THIS TOOL WHEN USERS: - Get a list of hosts - Filter hosts by various criteria (service, role, name, etc.) - Check host status and information <examples> Get all hosts (first 20) \. It is categorised as a Read tool in the Mackerel MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Mackerel MCP Server MCP server in PolicyLayer and add a rule for list_hosts: 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 Mackerel MCP Server. Nothing to install.
list_hosts 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_hosts 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_hosts. 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_hosts is provided by the Mackerel MCP Server MCP server (mackerelio-labs/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Mackerel MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
16 Mackerel MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.