AI agents call list_categories to retrieve information from Hong Kong Open Data MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves or lists available data categories from the Hong Kong open data portal, which is a read-only operation with no side effects. It enables discovery and querying of publicly available government data, consistent with the portal's purpose. Even though the tool description is empty, the name 'list_categories' and the broader server design strongly indicate a retrieval operation.
From the tool's definition Tool name 'list_categories' and server context indicating browsing of Hong Kong government's open data portal categories. Sibling tools include 'get_category_details', 'get_dataset_details', 'list_datasets', and 'search_datasets'—all read-only operations.
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 Hong Kong Open Data MCP Server, 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_categories. It is categorised as a Read tool in the Hong Kong Open Data MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Hong Kong Open Data MCP Server 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 Hong Kong Open Data MCP Server. 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 Hong Kong Open Data MCP Server MCP server (mcp-open-data-hk/mcp-open-data-hk). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Hong Kong Open Data MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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8 Hong Kong Open Data MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.