Plan a journey across London transport. from/to may be stop names, postcodes, or "lat,lon" coordinates. Returns journey options (legs, durations, modes). If a location is ambiguous, the API returns disambiguation options instead of journeys — refine the input or use a naptanId/coords.
Part of the Tfl server.
Free to start. No card required.
AI agents use plan_journey to create or modify resources in Tfl. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call plan_journey repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Tfl.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"plan_journey": {
"limits": [
{
"counter": "plan_journey_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Tfl policy for all 26 tools.
These attack patterns abuse exactly the kind of access plan_journey gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Plan a journey across London transport. from/to may be stop names, postcodes, or "lat,lon" coordinates. Returns journey options (legs, durations, modes). If a location is ambiguous, the API returns disambiguation options instead of journeys — refine the input or use a naptanId/coords.. It is categorised as a Write tool in the Tfl MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Tfl MCP server in PolicyLayer and add a rule for plan_journey: 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 Tfl. Nothing to install.
plan_journey is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the plan_journey 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. 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 is provided by the Tfl MCP server (https://gateway.pipeworx.io/tfl/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 26 Tfl tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
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