json_arrlen
Get the length of array at path. Args: key: The name of the key path: The path in the JSON document Returns: Array length or error message
This record as markdown: /tools/aws/json-arrlen.md
What json_arrlen does on AWS
AI agents call json_arrlen to retrieve information from AWS without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Why json_arrlen is rated Low
The tool queries and retrieves metadata (array length) from a JSON document without modifying, deleting, or executing anything. It is purely informational, making it a Read operation with low severity since misuse only exposes data structure information, not sensitive data directly.
From the tool's definition Tool description states 'Get the length of array at path' with args for key and path, returning 'Array length or error message'. This is a retrieval operation with no side effects.
Attacks that exploit this kind of access
The rule that runs json_arrlen 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_arrlen, this is the rule to start with:
json_arrlen is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect AWS, apply this rule, and every json_arrlen call is checked against it from then on.
Questions about json_arrlen
Get the length of array at path. Args: key: The name of the key path: The path in the JSON document Returns: Array length or error message. It is categorised as a Read tool in the AWS MCP Server, which means it retrieves data without modifying state.
Register the AWS 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 AWS. Nothing to install.
json_arrlen is a Read tool with low risk. Read-only tools are generally safe to allow by default.
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.
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.
json_arrlen 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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