Add one element to a HyperLogLog. Args: key: The name of the HyperLogLog key element: One element to add Returns: Success message or error message
AI agents use hll_add 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.
This tool creates or modifies data reversibly by adding an element to an in-memory or stored HyperLogLog structure. The operation is not destructive (no deletion), does not execute arbitrary code, and has minimal blast radius if misused by an AI agent—it would only add cardinality estimates to a counter. This is a typical Write operation.
From the tool's definition Tool name 'hll_add' and description 'Add one element to a HyperLogLog' indicate a data modification operation. HyperLogLog is a probabilistic data structure used for cardinality estimation, and 'add' modifies its state by inserting an element.
Documented attack patterns abuse exactly the kind of access hll_add gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and AWS, and nothing reaches the server without passing your rules. This is the rule we recommend for hll_add:
{
"version": "1",
"default": "deny",
"tools": {
"hll_add": {
"limits": [
{
"counter": "hll_add_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}hll_add 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.
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Add one element to a HyperLogLog. Args: key: The name of the HyperLogLog key element: One element to add 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.
Register the AWS MCP server in PolicyLayer and add a rule for hll_add: 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.
hll_add is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the hll_add 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.
Set action: deny in the PolicyLayer policy for hll_add. 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.
hll_add 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.
Start from AWS, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
300 AWS tools catalogued and risk-classified — across an index of 43,000+ MCP servers.