list_prometheus_label_values

THE RISK

Low Risk

Why list_prometheus_label_values needs a policy

This tool queries Prometheus datasource metadata (label values) and returns data without side effects. It is a read-only operation that retrieves observability data, fitting the 'Read' category for low-severity tools that simply fetch information.

From the tool's definition Tool name contains 'list' and description states 'List values for a specific label in a Prometheus datasource' — a retrieval operation with no modification or execution of external operations.

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

POLICY

How to control list_prometheus_label_values

PolicyLayer is an MCP gateway — it sits between your AI agents and Grafana FastMCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_prometheus_label_values:

policy.json

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

list_prometheus_label_values 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 Grafana FastMCP 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

Related tools and policies

More Grafana FastMCP Server tools

Execute find_error_pattern_logs Run the ErrorPatternLogs check via Sift and return the analysis result. Execute find_slow_requests Run the SlowRequests check via Sift and return the analysis result. Execute query_loki_logs Execute a LogQL query against a Loki datasource and return the matching log entries. Execute query_prometheus Execute PromQL queries against a Prometheus datasource. Write add_activity_to_incident Add a user note to an incident Write create_incident Create a new Grafana incident with the provided details. Write update_dashboard update_dashboard Read fetch fetch

All 45 Grafana FastMCP Server tools →

Read tools on other servers

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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 →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about list_prometheus_label_values

What does the list_prometheus_label_values tool do? +

List values for a specific label in a Prometheus datasource. It is categorised as a Read tool in the Grafana FastMCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on list_prometheus_label_values? +

Register the Grafana FastMCP Server MCP server in PolicyLayer and add a rule for list_prometheus_label_values: 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 Grafana FastMCP Server. Nothing to install.

What risk level is list_prometheus_label_values? +

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

Can I rate-limit list_prometheus_label_values? +

Yes. Add a rate_limit block to the list_prometheus_label_values 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_prometheus_label_values completely? +

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

list_prometheus_label_values is provided by the Grafana FastMCP Server MCP server (sandersouza/grafanafastmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Grafana FastMCP Server tool call.

Start from Grafana FastMCP 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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