string_set

THE RISK

Low Risk

Why string_set needs a policy

The description is empty, providing no information about what this tool does. The name 'string_set' alone is ambiguous - it could refer to setting a string value (Write), querying a string set data structure (Read), or something else entirely. Without further context, classification defaults to Other with low confidence. Severity is rated low due to the generic, non-specific name suggesting limited blast radius.

From the tool's definition Tool name is 'string_set' and description is empty or uninformative.

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

POLICY

How to control string_set

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "string_set": {
      "limits": [
        {
          "counter": "string_set_rate",
          "window": "minute",
          "max": 60,
          "scope": "grant"
        }
      ]
    }
  }
}

string_set gets a rate cap, and everything else on the server is denied unless you say otherwise.

Create a free account and register Prometheus 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.

SET A RULE FOR THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Tool risk categories → How PolicyLayer classifies MCP tools by what they can do.
MCP tool → What an MCP tool is and how clients discover and call it.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about string_set

What does the string_set tool do? +

string_set. It is categorised as a Other tool in the Prometheus MCP Server MCP Server, which means it performs auxiliary operations.

How do I enforce a policy on string_set? +

Register the Prometheus MCP Server MCP server in PolicyLayer and add a rule for string_set: 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 string_set? +

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

Can I rate-limit string_set? +

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

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

string_set is provided by the Prometheus MCP Server MCP server (awslabs.prometheus-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 Prometheus MCP Server tool call.

Start from Prometheus MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →