string_set

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/string-set.md

WHAT IT DOES

What string_set does on AWS

AI agents use string_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 string_set is rated Medium

This tool creates or modifies data in a key-value store (likely Redis given the parameter names ex/px/nx/xx/keepttl which are Redis SET command options). It is reversible (values can be overwritten or deleted), so it is Write rather than Destructive.

From the tool's definition Tool description states 'Set string value' with parameters to create or modify key-value pairs (key, value, ex, px, nx, xx, keepttl options). Returns 'Success message or error message' indicating a write operation.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs string_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 string_set, this is the rule to start with:

string_set Rate-limited

string_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": {
    "string_set": {
      "limits": [
        {
          "counter": "string_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 string_set call is checked against it from then on.

FAQ

Questions about string_set

What does the string_set tool do? +

Set string value. Args: key: The name of the key value: The value to set ex: Expire time in seconds px: Expire time in milliseconds nx: Only set if key does not exist xx: Only set if key exists keepttl: Retain the time to live associated with the key 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 string_set? +

Register the AWS MCP server in PolicyLayer and add a rule for string_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 string_set? +

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

Can I rate-limit string_set? +

Yes. Add a rate_limit block to the string_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 string_set completely? +

Set action: deny in the PolicyLayer policy for string_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 string_set? +

string_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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