json_arrlen

THE RISK

Low Risk

Why json_arrlen needs a policy

This tool performs a non-destructive, read-only operation. It queries a JSON structure to retrieve an array's length, with no side effects, data modification, deletion, or external system impact. The operation is purely informational and safe.

From the tool's definition Tool name 'json_arrlen' and description 'Get the length of array at path' indicate a simple query operation that retrieves the length property of a JSON array without modifying data.

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

POLICY

How to control json_arrlen

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

policy.json

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

json_arrlen 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 EKS 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 json_arrlen

What does the json_arrlen tool do? +

Get the length of array at path. It is categorised as a Read tool in the Amazon EKS MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on json_arrlen? +

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

What risk level is json_arrlen? +

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

Can I rate-limit json_arrlen? +

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

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

json_arrlen is provided by the Amazon EKS MCP Server MCP server (awslabs.eks-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 EKS MCP Server tool call.

Start from Amazon EKS 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 →