prom_query · Prometheus MCP Server MCP: Risk & Policy

WHAT IT DOES

What prom_query does on Prometheus MCP Server

AI agents invoke prom_query to trigger actions in Prometheus MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why prom_query needs a policy

Although Prometheus is a read-only metrics store, executing arbitrary PromQL expressions is an active operation that can be computationally expensive and trigger heavy server load. It falls under Execute rather than Read because it runs a query (which may be complex or resource-intensive) rather than simply fetching a known resource. No data is written or deleted, so severity is medium rather than high.

From the tool's definition "Execute a PromQL instant query" — the tool actively executes a query expression against Prometheus

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

prom_query Rate-limited

prom_query stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "prom_query": {
      "limits": [
        {
          "counter": "prom_query_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Prometheus MCP Server, so you can run agents against it safely.

FAQ

Questions about prom_query

What does the prom_query tool do? +

Execute a PromQL instant query. It is categorised as a Execute tool in the Prometheus MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on prom_query? +

Register the Prometheus MCP Server MCP server in PolicyLayer and add a rule for prom_query: 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 Prometheus MCP Server. Nothing to install.

What risk level is prom_query? +

prom_query is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit prom_query? +

Yes. Add a rate_limit block to the prom_query 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 prom_query completely? +

Set action: deny in the PolicyLayer policy for prom_query. 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 prom_query? +

prom_query is provided by the Prometheus MCP Server MCP server (yanmxa/prometheus-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.