json_numincrby

THE RISK

Medium Risk

Why json_numincrby needs a policy

This tool modifies data by incrementing a numeric value at a specified path, which is a reversible write operation. The tool name suggests JSON manipulation (likely Redis JSON or similar). While the description is minimal, incrementing a value is a write/update operation that doesn't permanently destroy data.

From the tool's definition Increment the number at path by value

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

POLICY

How to control json_numincrby

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_numincrby:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "json_numincrby": {
      "limits": [
        {
          "counter": "json_numincrby_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

json_numincrby 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.

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.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
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PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about json_numincrby

What does the json_numincrby tool do? +

Increment the number at path by value. It is categorised as a Write tool in the Amazon EKS MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on json_numincrby? +

Register the Amazon EKS MCP Server MCP server in PolicyLayer and add a rule for json_numincrby: 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_numincrby? +

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

Can I rate-limit json_numincrby? +

Yes. Add a rate_limit block to the json_numincrby 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_numincrby completely? +

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

json_numincrby 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 →