json_arrappend

Append values to the array at path. Args: key: The name of the key path: The path in the JSON document *values: One or more values to append Returns: New array length or error message

SERVERAWS SOURCE@awslabs/mcp

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity verified Pull the record →

This record as markdown: /tools/aws/json-arrappend.md

WHAT IT DOES

What json_arrappend does on AWS

AI agents use json_arrappend 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.

RISK

Why json_arrappend is rated Medium

This tool modifies an existing JSON document by appending values to an array at a specified path. It is a reversible write operation (values can be removed), so it falls under Write rather than Destructive. Medium severity because it can modify data in a JSON store, potentially affecting application state if misused.

From the tool's definition Append values to the array at path

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs json_arrappend safely

PolicyLayer is an MCP gateway: it sits between your AI agents and AWS, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For json_arrappend, this is the rule to start with:

json_arrappend Rate-limited

json_arrappend 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_arrappend": {
      "limits": [
        {
          "counter": "json_arrappend_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect AWS, apply this rule, and every json_arrappend call is checked against it from then on.

FAQ

Questions about json_arrappend

What does the json_arrappend tool do? +

Append values to the array at path. Args: key: The name of the key path: The path in the JSON document *values: One or more values to append Returns: New array length 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.

How do I enforce a policy on json_arrappend? +

Register the AWS MCP server in PolicyLayer and add a rule for json_arrappend: 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.

What risk level is json_arrappend? +

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

Can I rate-limit json_arrappend? +

Yes. Add a rate_limit block to the json_arrappend 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_arrappend completely? +

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

json_arrappend 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.

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