Get the number of keys in the object at path.
AI agents call json_objlen to retrieve information from AWS IoT SiteWise MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a simple read operation—counting keys in a JSON object at a specified path. It has no side effects, does not execute code or shell commands, does not modify data, and does not delete anything. The blast radius of misuse is minimal; an attacker could only learn the structure of JSON objects they already have access to.
From the tool's definition Tool name 'json_objlen' and description 'Get the number of keys in the object at path' indicate a retrieval operation that queries the structure of a JSON object without modifying, executing, or deleting anything.
Attacks that exploit this kind of access
Get the number of keys in the object at path. It is categorised as a Read tool in the AWS IoT SiteWise MCP Server MCP Server, which means it retrieves data without modifying state.
Register the AWS IoT SiteWise MCP Server MCP server in PolicyLayer and add a rule for json_objlen: 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 IoT SiteWise MCP Server. Nothing to install.
json_objlen 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_objlen 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_objlen. 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_objlen is provided by the AWS IoT SiteWise MCP Server MCP server (awslabs.aws-iot-sitewise-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.