hll_add · AWS IoT SiteWise MCP Server MCP: Risk & Policy

WHAT IT DOES

What hll_add does on AWS IoT SiteWise MCP Server

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

WHY IT NEEDS A POLICY

Why hll_add needs a policy

The tool creates or modifies data (adds an element to a HyperLogLog set). This is a Write operation rather than Read (which would only query) or Destructive (which cannot be undone). Severity is medium because while it modifies state, the impact is localized to a single HyperLogLog element addition, and the operation is reversible (the element could be removed).

From the tool's definition Tool description states 'Add one element to a HyperLogLog' — this modifies data by inserting an element into a HyperLogLog data structure, which is a reversible write operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

hll_add Rate-limited

hll_add 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": {
    "hll_add": {
      "limits": [
        {
          "counter": "hll_add_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 AWS IoT SiteWise MCP Server, so you can run agents against it safely.

FAQ

Questions about hll_add

What does the hll_add tool do? +

Add one element to a HyperLogLog. It is categorised as a Write tool in the AWS IoT SiteWise 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 hll_add? +

Register the AWS IoT SiteWise MCP Server MCP server in PolicyLayer and add a rule for hll_add: 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 AWS IoT SiteWise MCP Server. Nothing to install.

What risk level is hll_add? +

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

Can I rate-limit hll_add? +

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

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

hll_add is provided by the AWS IoT SiteWise MCP Server MCP server (awslabs.aws-iot-sitewise-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.