list_append · AWS Pricing MCP Server MCP: Risk & Policy

WHAT IT DOES

What list_append does on AWS Pricing MCP Server

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

WHY IT NEEDS A POLICY

Why list_append needs a policy

The tool description says it appends a value to a list, which is a write/modification operation. However, the description is very sparse and uninformative, and the context (an AWS Pricing MCP server) makes it unclear what list is being modified or whether this is a local in-memory operation or a persistent one. Confidence is lowered due to the vague description.

From the tool's definition 'Append value to list' — modifies a list by adding data

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

list_append Rate-limited

list_append 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": {
    "list_append": {
      "limits": [
        {
          "counter": "list_append_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 Pricing MCP Server, so you can run agents against it safely.

FAQ

Questions about list_append

What does the list_append tool do? +

Append value to list. It is categorised as a Write tool in the AWS Pricing 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 list_append? +

Register the AWS Pricing MCP Server MCP server in PolicyLayer and add a rule for list_append: 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 Pricing MCP Server. Nothing to install.

What risk level is list_append? +

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

Can I rate-limit list_append? +

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

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

list_append is provided by the AWS Pricing MCP Server MCP server (awslabs.aws-pricing-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.