Trip Planner — MCP Server + LangGraph Agent

A journey-planning MCP server built with FastMCP, plus a LangGraph agent that connects to it alongside two public MCP servers. The agent manages a traveller's itinerary: journeys (trips as a whole), the city stops within a journey, and the plan items (sights, meals, activities) within each stop.

Architecture

The user asks a question. The LangGraph agent thinks: if it needs a tool, it calls one, gets the result, and thinks again — repeating until it has enough to answer. MultiServerMCPClient connects to all three MCP servers when the agent starts and hands every discovered tool to the agent. One server is ours; two are public.

Related MCP server: Travel Planner MCP Server

Data model, tools, resource, prompt

SQLite, three tables, one nesting level each:

Tools (backend/mcpserver/TripPlannerServer.py) — full CRUD plus a live weather lookup:

Resources:

• journeys://all — one-line summary of every journey

• journey://{journey_id}/itinerary — templated resource, a day-by-day itinerary for one journey (each stop with its plan items underneath)

Prompt:

• suggest_itinerary(stop_id) — a reusable template that turns a stop's saved plan items into an hour-by-hour day plan

Public servers used, and why

• time (uvx mcp-server-time, stdio) — official reference MCP server for timezone/local-time lookups. Trivial, zero-risk, no genuine remote alternative exists for this, so stdio is the right call here.

• tavily (Streamable HTTP, https://mcp.tavily.com/mcp) — a genuinely hosted remote MCP server (no local process at all) from Tavily, a reputable company in the LLM tooling space (the same search backend LangChain's own community tools use). It needs a free API key (tavily.com, no credit card). Picked over a plain page-fetch server because it does real-time, ranked web search (attractions, travel advisories, local facts) rather than fetching one raw page — a much stronger fit for a trip planner. Deliberately avoided pulling a server from the public MCP registries (registry.modelcontextprotocol.io, Smithery, Glama) directly — those directories are unvetted, and searching them turned up entries with suspicious names during development. Tavily is a known, reputable company with a real product, not an anonymous registry listing.

Extras beyond the core CRUD flow

• get_destination_weather calls the free Open-Meteo API from inside a tool (geocoding + current weather, no key required).

• backend/integrations/fastapimcp_integration.py serves REST (/health, /journeys) and MCP (/mcp) from one FastAPI ASGI app.

• add_stop logs via ctx.info(...), visible live in the MCP Inspector's notification panel.

How to run it

1. Install dependencies (uses uv):

   uv sync

2. Copy .env.example to .env and fill in:

   OPENAI_API_KEY=sk-...
   TAVILY_API_KEY=tvly-...      # free key at https://tavily.com

3. Start the server (terminal 1):

   uv run backend/mcpserver/TripPlannerServer.py

   Live at http://127.0.0.1:8000/mcp (note the required /mcp suffix).

   Optional — run the combined REST+MCP app instead:

   uv run python -m backend.integrations.fastapimcp_integration

4. Run the agent (terminal 2):

   uv run backend/client/langgraphagent.py "Add a 3-night stop in Kyoto to journey 1 and tell me the local time there"

5. Optional — test the server directly in the MCP Inspector before running the agent:

   npx @modelcontextprotocol/inspector

   Transport: Streamable HTTP, URL: http://127.0.0.1:8000/mcp.

Requires uv (Python/uvx) and Node.js (npx, for the Inspector) installed.

Example runs

Full tool-call traces are in screenshots/demo.txt. Summary:

1. Write-only — "Create a new journey called 'Bali Getaway' from Mumbai, budget 1500, dates 2026-09-01 to 2026-09-10. Then add a 5-night stop in Bali, Indonesia to it." → Created journey #3 and stop #4 on our server.

2. Write + public time — "Add a 4-night stop in Reykjavik, Iceland to journey 3, and tell me the current local time there." → Added stop #5, and called get_current_time (both tool calls fired in parallel in one turn) → 11:03, Saturday, Atlantic/Reykjavik (UTC+0).

3. Public tavily research — "What are the top attractions to see in Reykjavik right now, and are there any current travel advisories for Iceland?" → Real-time web search returned 8 ranked attractions and 3 current government travel advisories, with live sources.

Why an MCP server instead of plain Python functions in the agent?

Putting tools in an MCP server decouples what a tool can do from which agent uses it. The same trip_planner server can be called by this LangGraph agent, tested by hand in the MCP Inspector, or plugged into a completely different agent or client later, all without touching the tool code — because the server exposes a stable, self-describing contract (schemas generated straight from function signatures and docstrings) over a standard protocol, instead of being tangled into one agent's Python process. It also means the server can run, scale, and fail independently of the agent: if the trip-planner logic needs a different host, a different language, or its own deployment schedule, that's an infrastructure change, not a rewrite. Writing the same logic as inline Python functions works fine for a single throwaway script, but it locks the tool to that one agent and gives up all of that reuse, isolation, and discoverability for no benefit.

Video walkthrough

(link to be added)