json_arrtrim · AWS Labs postgres MCP Server MCP

WHAT IT DOES

What json_arrtrim does on AWS Labs postgres MCP Server

AI agents use json_arrtrim to create or update resources in AWS Labs postgres MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your AWS Labs postgres MCP Server environment.

WHY IT NEEDS A POLICY

Why json_arrtrim needs a policy

Trimming an array modifies the data by removing elements outside the specified range. This is a reversible write operation (data is modified but the operation doesn't irreversibly destroy the database structure). The blast radius is medium as an AI agent could accidentally trim arrays to unintended ranges, losing data within a JSON document.

From the tool's definition Trim array at path to include only elements within range

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

json_arrtrim Rate-limited

json_arrtrim 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": {
    "json_arrtrim": {
      "limits": [
        {
          "counter": "json_arrtrim_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches AWS Labs postgres MCP Server, so you can run agents against it safely.

FAQ

Questions about json_arrtrim

What does the json_arrtrim tool do? +

Trim array at path to include only elements within range. It is categorised as a Write tool in the AWS Labs postgres 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_arrtrim? +

Register the AWS Labs postgres MCP Server MCP server in PolicyLayer and add a rule for json_arrtrim: 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 Labs postgres MCP Server. Nothing to install.

What risk level is json_arrtrim? +

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

Can I rate-limit json_arrtrim? +

Yes. Add a rate_limit block to the json_arrtrim 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_arrtrim completely? +

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

json_arrtrim is provided by the AWS Labs postgres MCP Server MCP server (awslabs.postgres-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.