add_extras · Mcp Hertz MCP: Risk & Policy

WHAT IT DOES

What add_extras does on Mcp Hertz

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

WHY IT NEEDS A POLICY

Why add_extras needs a policy

This tool creates or modifies data reversibly within an existing reservation (Write category). Severity is medium because misuse could result in unwanted charges or financial obligations if an agent adds expensive extras without authorization, but the changes can be reversed (extras can be removed).

From the tool's definition Tool adds optional extras to an existing reservation—modifying the reservation by attaching additional services. The description explicitly states 'Add optional extras...to an existing reservation,' which is a modification operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_extras Rate-limited

add_extras 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": {
    "add_extras": {
      "limits": [
        {
          "counter": "add_extras_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 Hertz, so you can run agents against it safely.

FAQ

Questions about add_extras

What does the add_extras tool do? +

Add optional extras (GPS, child seats, additional drivers, roadside assistance, etc.) to an existing reservation. It is categorised as a Write tool in the Mcp Hertz MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_extras? +

Register the Mcp Hertz MCP server in PolicyLayer and add a rule for add_extras: 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 Hertz. Nothing to install.

What risk level is add_extras? +

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

Can I rate-limit add_extras? +

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

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

add_extras is provided by the Mcp Hertz MCP server (markswendsen-code/mcp-hertz). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.