list_prepend

Prepend value to list. Args: key: The name of the key value: The value to prepend Returns: Success message or error message

SERVERAWS SOURCE@awslabs/mcp

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity verified Pull the record →

This record as markdown: /tools/aws/list-prepend.md

WHAT IT DOES

What list_prepend does on AWS

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

RISK

Why list_prepend is rated Medium

The tool modifies an existing list by prepending a value to it. This is a reversible write operation (the prepended value can be removed), not destructive. The blast radius is medium as it could corrupt list data structures if misused.

From the tool's definition Prepend value to list

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs list_prepend safely

PolicyLayer is an MCP gateway: it sits between your AI agents and AWS, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For list_prepend, this is the rule to start with:

list_prepend Rate-limited

list_prepend 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_prepend": {
      "limits": [
        {
          "counter": "list_prepend_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect AWS, apply this rule, and every list_prepend call is checked against it from then on.

FAQ

Questions about list_prepend

What does the list_prepend tool do? +

Prepend value to list. Args: key: The name of the key value: The value to prepend Returns: Success message or error message. It is categorised as a Write tool in the AWS 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_prepend? +

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

What risk level is list_prepend? +

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

Can I rate-limit list_prepend? +

Yes. Add a rate_limit block to the list_prepend 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_prepend completely? +

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

list_prepend is provided by the AWS MCP server (@awslabs/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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