update_persistent_info · Simple MCP: Risk & Policy

WHAT IT DOES

What update_persistent_info does on Simple MCP

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

WHY IT NEEDS A POLICY

Why update_persistent_info needs a policy

This is a Write operation because it creates or modifies data (key-value pairs in persistent storage) in a reversible manner. It does not execute arbitrary code, delete data, or create financial obligations.

From the tool's definition Tool description states it 'Update or add a key-value pair to the persistent info JSON file' — this directly modifies stored data. The verbs 'update' and 'add' indicate reversible creation or modification of data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_persistent_info Rate-limited

update_persistent_info 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": {
    "update_persistent_info": {
      "limits": [
        {
          "counter": "update_persistent_info_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, so you can run agents against it safely.

FAQ

Questions about update_persistent_info

What does the update_persistent_info tool do? +

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

How do I enforce a policy on update_persistent_info? +

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

What risk level is update_persistent_info? +

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

Can I rate-limit update_persistent_info? +

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

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

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