hash_set_if_not_exists

Set field in hash only if it does not exist. Args: key: The name of the key field: The field name 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/hash-set-if-not-exists.md

WHAT IT DOES

What hash_set_if_not_exists does on AWS

AI agents use hash_set_if_not_exists 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 hash_set_if_not_exists is rated Medium

The tool creates or modifies data in a reversible manner (hash field set operation), which is the defining characteristic of Write. It is not Read (no retrieval without side effects), not Execute (not running arbitrary code/commands), not Destructive (the operation is reversible), not Financial (no money movement), and not Other.

From the tool's definition Tool description states 'Set field in hash only if it does not exist' with parameters key, field, and value.

Attacks that exploit this kind of access

RECOMMENDED RULE

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

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.

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

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. Args: key: The name of the key field: The field name 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 hash_set_if_not_exists? +

Register the AWS 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. 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 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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