list_set

Set value at index in list. Args: key: The name of the key index: The index (0-based, negative indices supported) value: The value to set 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-set.md

WHAT IT DOES

What list_set does on AWS

AI agents use list_set 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_set is rated Medium

The tool writes/updates a value in a list data structure at a given index. Despite being named 'list_set', the description confirms it sets (overwrites) a value, which is a reversible write operation. Confidence is slightly reduced because the description contradicts the name ('list_set' vs 'Set value at index in list'), and the server context (AWS) is unclear for this Redis-like list operation.

From the tool's definition 'Set value at index in list' — modifies an existing list element at a specified index

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs list_set 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_set, this is the rule to start with:

list_set Rate-limited

list_set 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_set": {
      "limits": [
        {
          "counter": "list_set_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_set call is checked against it from then on.

FAQ

Questions about list_set

What does the list_set tool do? +

Set value at index in list. Args: key: The name of the key index: The index (0-based, negative indices supported) value: The value to set 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_set? +

Register the AWS MCP server in PolicyLayer and add a rule for list_set: 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_set? +

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

Can I rate-limit list_set? +

Yes. Add a rate_limit block to the list_set 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_set completely? +

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

list_set 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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