set_value · Simple MCP Server MCP: Risk & Policy

WHAT IT DOES

What set_value does on Simple MCP Server

AI agents use set_value to create or update resources in Simple MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Simple MCP Server environment.

WHY IT NEEDS A POLICY

Why set_value needs a policy

The tool creates or modifies data (a key-value pair) but does not irreversibly delete data, execute arbitrary code, or involve financial transactions. The operation is reversible via the 'delete_value' or 'clear_values' sibling tools. The in-memory nature and lightweight design limit blast radius. Severity is low because impact is confined to application state without external side effects.

From the tool's definition Tool name 'set_value' and description 'Set a key-value pair in the store' indicate reversible creation/modification of data in an in-memory key-value store.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_value Rate-limited

set_value stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_value": {
      "limits": [
        {
          "counter": "set_value_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about set_value

What does the set_value tool do? +

Set a key-value pair in the store. It is categorised as a Write tool in the Simple MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_value? +

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

What risk level is set_value? +

set_value is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit set_value? +

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

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

set_value is provided by the Simple MCP Server MCP server (jmgress/simple-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.