list_monitors

Retrieve all monitor configurations from Mackerel. 🔍 USE THIS TOOL WHEN USERS: - Get a list of all monitors - View monitor configurations <examples> Get all monitors \

ServerMackerel MCP Server
CategoryRead

How to control list_monitors ↓

WHAT IT DOES

What list_monitors does on Mackerel MCP Server

AI agents call list_monitors 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.

THE RISK

Low Risk

Why list_monitors needs a policy

This tool retrieves and queries monitoring configuration data without creating, modifying, deleting, or executing any operations. It is a straightforward read operation with minimal blast radius if misused by an AI agent—the worst outcome would be information disclosure of existing monitor settings.

From the tool's definition Tool name is 'list_monitors' and description states 'Retrieve all monitor configurations from Mackerel.' The use cases explicitly mention 'Get a list of all monitors' and 'View monitor configurations,' which are read-only operations with no side effects.

Documented attack patterns abuse exactly the kind of access list_monitors gives an agent:

POLICY

How to control list_monitors

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_monitors:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "list_monitors": {}
  }
}

list_monitors is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Mackerel MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

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EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
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FAQ

Questions about list_monitors

What does the list_monitors tool do? +

Retrieve all monitor configurations from Mackerel. 🔍 USE THIS TOOL WHEN USERS: - Get a list of all monitors - View monitor configurations <examples> Get all monitors \. It is categorised as a Read tool in the Mackerel MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on list_monitors? +

Register the Mackerel MCP Server MCP server in PolicyLayer and add a rule for list_monitors: 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.

What risk level is list_monitors? +

list_monitors is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit list_monitors? +

Yes. Add a rate_limit block to the list_monitors 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.

How do I block list_monitors completely? +

Set action: deny in the PolicyLayer policy for list_monitors. 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.

What MCP server provides list_monitors? +

list_monitors 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.

Enforce policy on every Mackerel MCP Server tool call.

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.

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