modify_reservation · Mcp Hertz MCP: Risk & Policy

WHAT IT DOES

What modify_reservation does on Mcp Hertz

AI agents use modify_reservation 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 modify_reservation needs a policy

This tool creates or modifies data (a reservation) in a reversible manner. It does not delete data (would be Destructive), execute arbitrary code (would be Execute), or move money (would be Financial).

From the tool's definition Tool name is 'modify_reservation' and description states it enables changing 'dates, locations, or vehicle class' on an existing reservation — these are reversible modifications to booking data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

modify_reservation Rate-limited

modify_reservation 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": {
    "modify_reservation": {
      "limits": [
        {
          "counter": "modify_reservation_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 modify_reservation

What does the modify_reservation tool do? +

Modify an existing Hertz reservation — change dates, locations, or vehicle class. 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 modify_reservation? +

Register the Mcp Hertz MCP server in PolicyLayer and add a rule for modify_reservation: 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 modify_reservation? +

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

Can I rate-limit modify_reservation? +

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

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

modify_reservation 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.