List all document categories with their document counts. Read-only. No side effects. Reflects the live index state. Returns: JSON string with category names, document counts per category, and total document count. Usage: Use before filtering search_knowledge() or list_documents() by category to s...
AI agents call list_categories to retrieve information from Knowledge Rag without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This is a straightforward read operation that retrieves and presents index metadata. It has no capability to modify, delete, or execute operations. The blast radius if misused by an agent is minimal—it can only expose the organizational structure of indexed documents, which is non-sensitive catalog information useful for navigating the knowledge base.
From the tool's definition Tool explicitly described as 'Read-only. No side effects.' Returns only metadata about document categories and counts from the live index.
Risk signalsBulk/mass operation — affects multiple targets
Documented attack patterns abuse exactly the kind of access list_categories gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Knowledge Rag, and nothing reaches the server without passing your rules. This is the rule we recommend for list_categories:
{
"version": "1",
"default": "deny",
"tools": {
"list_categories": {}
}
}list_categories is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List all document categories with their document counts. Read-only. No side effects. Reflects the live index state. Returns: JSON string with category names, document counts per category, and total document count. Usage: Use before filtering search_knowledge() or list_documents() by category to see which categories exist and how many documents each contains. Use get_index_stats() instead for broader system health metrics (model name, cache hit rate, BM25 status). It is categorised as a Read tool in the Knowledge Rag MCP Server, which means it retrieves data without modifying state.
Register the Knowledge Rag 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 Knowledge Rag. 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 Knowledge Rag MCP server (lyonzin/knowledge-rag). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Knowledge Rag, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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12 Knowledge Rag tools catalogued and risk-classified — across an index of 43,000+ MCP servers.