hash_set_if_not_exists · AWS IoT SiteWise MCP Server MCP

WHAT IT DOES

What hash_set_if_not_exists does on AWS IoT SiteWise MCP Server

AI agents use hash_set_if_not_exists 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 hash_set_if_not_exists needs a policy

This tool creates or modifies data (sets a field value) with a conditional check. It is reversible (the field can be updated or deleted later), making it a Write operation. Severity is medium because unintended field creation in a hash could corrupt data structures or inject malicious values into application state, but the operation is not irreversible.

From the tool's definition Tool name 'hash_set_if_not_exists' and description 'Set field in hash only if it does not exist' indicate conditional creation/modification of data in a hash structure.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

hash_set_if_not_exists Rate-limited

hash_set_if_not_exists 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": {
    "hash_set_if_not_exists": {
      "limits": [
        {
          "counter": "hash_set_if_not_exists_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 hash_set_if_not_exists

What does the hash_set_if_not_exists tool do? +

Set field in hash only if it does not exist. 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 hash_set_if_not_exists? +

Register the AWS IoT SiteWise MCP Server MCP server in PolicyLayer and add a rule for hash_set_if_not_exists: 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 hash_set_if_not_exists? +

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

Can I rate-limit hash_set_if_not_exists? +

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

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

hash_set_if_not_exists 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.