AI agents call plan_journey_by_city_names to retrieve information from SNCF API MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Based on the tool name and server description focused on 'journey planning and train information retrieval', this tool likely queries the SNCF API to return journey options between cities without side effects. The sibling tools (check_disruptions, get_station_details, get_station_schedule) are all read operations, consistent with this being a Read tool. Confidence is reduced due to the empty description.
From the tool's definition Tool name 'plan_journey_by_city_names' and server context of journey planning/train information retrieval suggest a read-only query operation. Description is empty.
Documented attack patterns abuse exactly the kind of access plan_journey_by_city_names gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and SNCF API MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for plan_journey_by_city_names:
{
"version": "1",
"default": "deny",
"tools": {
"plan_journey_by_city_names": {}
}
}plan_journey_by_city_names is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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plan_journey_by_city_names. It is categorised as a Read tool in the SNCF API MCP Server MCP Server, which means it retrieves data without modifying state.
Register the SNCF API MCP Server MCP server in PolicyLayer and add a rule for plan_journey_by_city_names: 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 SNCF API MCP Server. Nothing to install.
plan_journey_by_city_names 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 plan_journey_by_city_names 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 plan_journey_by_city_names. 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.
plan_journey_by_city_names is provided by the SNCF API MCP Server MCP server (kryzo/mcp-sncf). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from SNCF API 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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4 SNCF API MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.