instant-query · Prometheus MCP: Risk & Policy

WHAT IT DOES

What instant-query does on Prometheus

AI agents invoke instant-query to trigger actions in Prometheus. 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 instant-query needs a policy

This tool executes a query against an external Prometheus system. While it is primarily read-oriented (retrieving metrics data), it actively executes PromQL expressions against a live datasource rather than passively fetching static data. PromQL can be complex and resource-intensive, and the execution runs against an external system.

From the tool's definition "Execute an instant Prometheus query" — the tool runs a PromQL query against a live Prometheus instance

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

instant-query Rate-limited

instant-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": {
    "instant-query": {
      "limits": [
        {
          "counter": "instant-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, so you can run agents against it safely.

FAQ

Questions about instant-query

What does the instant-query tool do? +

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

How do I enforce a policy on instant-query? +

Register the Prometheus MCP server in PolicyLayer and add a rule for instant-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. Nothing to install.

What risk level is instant-query? +

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

Can I rate-limit instant-query? +

Yes. Add a rate_limit block to the instant-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 instant-query completely? +

Set action: deny in the PolicyLayer policy for instant-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 instant-query? +

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