json_objlen
Get the number of keys in the object at path. Args: key: The name of the key path: The path in the JSON document Returns: Number of keys or error message
This record as markdown: /tools/aws/json-objlen.md
What json_objlen does on AWS
AI agents call json_objlen 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_objlen is rated Low
The tool performs a simple introspection of JSON data structure (counting keys), which is a read operation with no side effects. No data is modified, deleted, or executed. The blast radius of misuse is minimal—an agent could only learn the structure of JSON objects it has access to read.
From the tool's definition Tool description states 'Get the number of keys in the object at path' with return value 'Number of keys or error message'. This is a read-only query operation that retrieves metadata about a JSON structure without modifying, executing, or deleting anything.
Attacks that exploit this kind of access
The rule that runs json_objlen 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_objlen, this is the rule to start with:
json_objlen 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_objlen call is checked against it from then on.
Questions about json_objlen
Get the number of keys in the object at path. Args: key: The name of the key path: The path in the JSON document Returns: Number of keys 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_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. 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 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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