hll_count

THE RISK

Low Risk

Why hll_count needs a policy

This is a read-only operation that retrieves cardinality estimates from a HyperLogLog data structure. It retrieves or queries data with no side effects, fitting the Read category. The severity is low because misuse would only return potentially incorrect cardinality estimates without affecting data integrity or enabling harmful operations.

From the tool's definition Tool name 'hll_count' and description 'Get the estimated cardinality of a HyperLogLog' indicate a retrieval operation that queries data structure statistics without modification or execution of arbitrary operations.

Documented attack patterns abuse exactly the kind of access hll_count gives an agent:

POLICY

How to control hll_count

PolicyLayer is an MCP gateway — it sits between your AI agents and Amazon Redshift MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for hll_count:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "hll_count": {}
  }
}

hll_count is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Amazon Redshift MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

Roll out MCP under one policy → Per-person scoped tokens, one central policy, and full audit across every server your team connects.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about hll_count

What does the hll_count tool do? +

Get the estimated cardinality of a HyperLogLog. It is categorised as a Read tool in the Amazon Redshift MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on hll_count? +

Register the Amazon Redshift MCP Server MCP server in PolicyLayer and add a rule for hll_count: 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 Amazon Redshift MCP Server. Nothing to install.

What risk level is hll_count? +

hll_count is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit hll_count? +

Yes. Add a rate_limit block to the hll_count 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 hll_count completely? +

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

hll_count is provided by the Amazon Redshift MCP Server MCP server (awslabs.redshift-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Amazon Redshift MCP Server tool call.

Start from Amazon Redshift MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →