manage_custom_rules · MCP Shamash MCP: Risk & Policy

WHAT IT DOES

What manage_custom_rules does on MCP Shamash

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

WHY IT NEEDS A POLICY

Why manage_custom_rules needs a policy

This tool creates or modifies security rules, which are configuration artifacts. While it can change security posture, the blast radius is limited to rule definitions rather than production data or systems. The tool does not execute external operations (Execute), destroy data irreversibly (Destructive), or move money (Financial).

From the tool's definition Tool name 'manage_custom_rules' and description 'Manage custom security rules' indicate creation, modification, or deletion of security rule configurations. 'Manage' typically encompasses write operations (create, update, delete) on rule definitions.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

manage_custom_rules Rate-limited

manage_custom_rules 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": {
    "manage_custom_rules": {
      "limits": [
        {
          "counter": "manage_custom_rules_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 MCP Shamash, so you can run agents against it safely.

FAQ

Questions about manage_custom_rules

What does the manage_custom_rules tool do? +

Manage custom security rules. It is categorised as a Write tool in the MCP Shamash MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on manage_custom_rules? +

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

What risk level is manage_custom_rules? +

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

Can I rate-limit manage_custom_rules? +

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

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

manage_custom_rules is provided by the MCP Shamash MCP server (neotecdigital/mcp_shamash). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.