AI agents call list_categories to retrieve information from Ynab without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves and displays existing budget category data. It performs a read-only query operation ('List') with no capability to create, modify, delete, or execute actions. The minimal blast radius and lack of side effects place it in the Read category with low severity.
From the tool's definition Tool name 'list_categories' and description 'List all categories grouped by category group for a budget' indicate data retrieval with no modification or side effects.
Attacks that exploit this kind of access
[1 API call] List all categories grouped by category group for a budget. It is categorised as a Read tool in the Ynab MCP Server, which means it retrieves data without modifying state.
Register the Ynab MCP server in PolicyLayer and add a rule for list_categories: 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 Ynab. Nothing to install.
list_categories 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 list_categories 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 list_categories. 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.
list_categories is provided by the Ynab MCP server (justmytwospence/ynab-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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