PoC setting up a MCP for trip planning

config/config.exs

@@ -87,4 +87,8 @@ config :sentry,
   root_source_code_paths: [File.cwd!()],
   context_lines: 5
 
+config :vancouver,
+  name: "MBTA MCP",
+  version: "1.0.0"
+
 import_config "#{config_env()}.exs"

lib/dotcom/tools/plan_trip.ex

@@ -0,0 +1,104 @@
+defmodule Dotcom.Tools.PlanTrip do
+  use Vancouver.Tool
+
+  @otp_module Application.compile_env!(:dotcom, :otp_module)
+  @params %OpenTripPlannerClient.PlanParams{
+    fromPlace: "South Station::42.352271,-71.055242",
+    toPlace: "North Station::42.365577,-71.06129",
+    date: "2025-06-25",
+    time: "12:00pm",
+    arriveBy: false,
+    numItineraries: 100,
+    transportModes: [
+      # %{mode: :TRAM},
+      %{mode: :SUBWAY},
+      # %{mode: :BUS},
+      # %{mode: :FERRY},
+      # %{mode: :RAIL}
+    ],
+    wheelchair: false
+  }
+
+  def name, do: "plan_trip"
+  def description, do: "Plan a trip in Boston from A to B"
+
+  def input_schema do
+    %{
+      "type" => "object",
+      "properties" => %{
+        "from" => %{"type" => "string"},
+        "to" => %{"type" => "string"}
+      },
+      "required" => ["from", "to"]
+    }
+  end
+
+  def run(conn, %{"from" => _, "to" => _}) do
+    {:ok, [%OpenTripPlannerClient.ItineraryGroup{itineraries: itineraries} | _]} = @otp_module.plan(@params)
+
+    summary_string = itineraries |> List.first() |> itinerary_to_summary_string()
+    link_string = link_string(@params)
+    itineraries_strings = itineraries_to_strings(itineraries) |> List.last()
+
+    send_text(conn, summary_string <> link_string <> itineraries_strings)
+  end
+
+  defp distance(feet) when feet < 528 do
+    "a very short distance"
+  end
+
+  defp distance(feet) do
+    feet / 5280
+    |> Float.round(1)
+    |> Float.to_string()
+    |> Kernel.<>(" miles")
+  end
+
+  defp duration(seconds) do
+    minutes = seconds |> round() |> div(60)
+
+    if minutes < 60 do
+      "#{minutes} minutes"
+    else
+      hours = div(minutes, 60)
+      remaining_minutes = rem(minutes, 60)
+      "#{hours} hours #{remaining_minutes} minutes"
+    end
+  end
+
+  defp itineraries_to_strings(itineraries) when is_binary(itineraries) do
+    [itineraries]
+  end
+
+  defp itineraries_to_strings(itineraries) when is_list(itineraries) do
+    Enum.map(itineraries, &itinerary_to_string/1)
+  end
+
+  defp itinerary_to_string(itinerary) do
+    Enum.map(itinerary.legs, &leg_to_string/1) |> Enum.join("\n")
+  end
+
+  defp itinerary_to_summary_string(itinerary) do
+    tag = itinerary.tag |> Atom.to_string() |> Recase.to_title()
+
+    "The most #{tag} route will take #{duration(itinerary.duration)}.\n"
+  end
+
+  defp leg_to_string(%{mode: :WALK} = leg) do
+    "Walk #{distance(leg.distance)} #{leg.from.name} from #{leg.to.name}"
+  end
+
+  defp leg_to_string(%{mode: :BUS} = leg) do
+    "Ride the #{leg.route.short_name} bus for #{duration(leg.duration)} from #{leg.from.name} to #{leg.to.name}"
+  end
+
+  defp leg_to_string(leg) do
+    "Take the #{leg.route.long_name} from #{leg.from.name} to #{leg.to.name} for approximately #{duration(leg.duration)}"
+  end
+
+  defp link_string(params) do
+    encoded = Dotcom.TripPlan.AntiCorruptionLayer.encode(params)
+
+    "Visit MBTA's [Trip Planner](https://www.mbta.com/trip-planner?plan=#{encoded}) for more details.\n"
+  end
+end

lib/dotcom_web/router.ex

@@ -61,6 +61,8 @@ defmodule DotcomWeb.Router do
     plug(DotcomWeb.Plugs.CacheControl, max_age: 86_400)
   end
 
+  forward "/mcp", Vancouver.Router, tools: [Dotcom.Tools.PlanTrip]
+
   scope "/", DotcomWeb do
     # no pipe
     get("/_health", HealthController, :index)

mix.exs

@@ -160,6 +160,7 @@ defmodule DotCom.Mixfile do
       {:typed_ecto_schema, "0.4.1"},
       {:unrooted_polytree, "0.1.1"},
       {:uuid, "1.1.8"},
+      {:vancouver, "0.3.0"},
       {:wallaby, "0.30.10", [runtime: false, only: [:dev, :test]]},
       {:yaml_elixir, "2.11.0", only: [:dev]},
       {:ymlr, "5.1.3", only: [:dev]}

mix.lock

@@ -32,6 +32,7 @@
   "elixir_make": {:hex, :elixir_make, "0.9.0", "6484b3cd8c0cee58f09f05ecaf1a140a8c97670671a6a0e7ab4dc326c3109726", [:mix], [], "hexpm", "db23d4fd8b757462ad02f8aa73431a426fe6671c80b200d9710caf3d1dd0ffdb"},
   "erlex": {:hex, :erlex, "0.2.7", "810e8725f96ab74d17aac676e748627a07bc87eb950d2b83acd29dc047a30595", [:mix], [], "hexpm", "3ed95f79d1a844c3f6bf0cea61e0d5612a42ce56da9c03f01df538685365efb0"},
   "ex_doc": {:hex, :ex_doc, "0.38.2", "504d25eef296b4dec3b8e33e810bc8b5344d565998cd83914ffe1b8503737c02", [:mix], [{:earmark_parser, "~> 1.4.44", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_c, ">= 0.1.0", [hex: :makeup_c, repo: "hexpm", optional: true]}, {:makeup_elixir, "~> 0.14 or ~> 1.0", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1 or ~> 1.0", [hex: :makeup_erlang, repo: "hexpm", optional: false]}, {:makeup_html, ">= 0.1.0", [hex: :makeup_html, repo: "hexpm", optional: true]}], "hexpm", "732f2d972e42c116a70802f9898c51b54916e542cc50968ac6980512ec90f42b"},
+  "ex_json_schema": {:hex, :ex_json_schema, "0.11.1", "b593f92937a095f66054bb318681397dfe7304e7d2b6b1a7534ea3aa40024f8c", [:mix], [{:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}], "hexpm", "32d651a575a6ce2fd613f140b0fef8dd0acc7cf8e8bcd29a3a1be5c945700dd5"},
   "ex_machina": {:hex, :ex_machina, "2.8.0", "a0e847b5712065055ec3255840e2c78ef9366634d62390839d4880483be38abe", [:mix], [{:ecto, "~> 2.2 or ~> 3.0", [hex: :ecto, repo: "hexpm", optional: true]}, {:ecto_sql, "~> 3.0", [hex: :ecto_sql, repo: "hexpm", optional: true]}], "hexpm", "79fe1a9c64c0c1c1fab6c4fa5d871682cb90de5885320c187d117004627a7729"},
   "ex_unit_summary": {:hex, :ex_unit_summary, "0.1.0", "7b0352afc5e6a933c805df0a539b66b392ac12ba74d8b208db7d83f77cb57049", [:mix], [], "hexpm", "8c87d0deade3657102902251d2ec60b5b94560004ce0e2c2fa5b466232716bd6"},
   "excoveralls": {:hex, :excoveralls, "0.18.5", "e229d0a65982613332ec30f07940038fe451a2e5b29bce2a5022165f0c9b157e", [:mix], [{:castore, "~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "523fe8a15603f86d64852aab2abe8ddbd78e68579c8525ae765facc5eae01562"},
@@ -134,6 +135,7 @@
   "unicode_util_compat": {:hex, :unicode_util_compat, "0.7.1", "a48703a25c170eedadca83b11e88985af08d35f37c6f664d6dcfb106a97782fc", [:rebar3], [], "hexpm", "b3a917854ce3ae233619744ad1e0102e05673136776fb2fa76234f3e03b23642"},
   "unrooted_polytree": {:hex, :unrooted_polytree, "0.1.1", "95027b1619d707fcbbd8980708a50efd170782142dd3de5112e9332d4cc27fef", [:mix], [], "hexpm", "9c8143d2015526ae49c3642ca509802e4db129685a57a0ec413e66546fe0c251"},
   "uuid": {:hex, :uuid, "1.1.8", "e22fc04499de0de3ed1116b770c7737779f226ceefa0badb3592e64d5cfb4eb9", [:mix], [], "hexpm", "c790593b4c3b601f5dc2378baae7efaf5b3d73c4c6456ba85759905be792f2ac"},
+  "vancouver": {:hex, :vancouver, "0.3.0", "2bf3920e97bf98a79440fbafe3a1cdb936aa45ca4b34ab393f98855d18ccbb09", [:mix], [{:ex_json_schema, "~> 0.11", [hex: :ex_json_schema, repo: "hexpm", optional: false]}, {:plug, "~> 1.15", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm", "d050b9864b833528dc9c87c5d3d2f6a36c0a070130053e2a7e5fae79c618c4fe"},
   "vector": {:hex, :vector, "1.1.0", "0789b5e00e9c551d8d5880acab9a8f44ed46690d083af397018bf0c7f30c1092", [:mix], [], "hexpm", "48b0a800ec88e55b12c689b09100e4c9ba41ea1befb459221c085a4e70040696"},
   "wallaby": {:hex, :wallaby, "0.30.10", "574afb8796521252daf49a4cd76a1c389d53cae5897f2d4b5f55dfae159c8e50", [:mix], [{:ecto_sql, ">= 3.0.0", [hex: :ecto_sql, repo: "hexpm", optional: true]}, {:httpoison, "~> 0.12 or ~> 1.0 or ~> 2.0", [hex: :httpoison, repo: "hexpm", optional: false]}, {:jason, "~> 1.1", [hex: :jason, repo: "hexpm", optional: false]}, {:phoenix_ecto, ">= 3.0.0", [hex: :phoenix_ecto, repo: "hexpm", optional: true]}, {:web_driver_client, "~> 0.2.0", [hex: :web_driver_client, repo: "hexpm", optional: false]}], "hexpm", "a8f89b92d8acce37a94b5dfae6075c2ef00cb3689d6333f5f36c04b381c077b2"},
   "web_driver_client": {:hex, :web_driver_client, "0.2.0", "63b76cd9eb3b0716ec5467a0f8bead73d3d9612e63f7560d21357f03ad86e31a", [:mix], [{:hackney, "~> 1.6", [hex: :hackney, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}, {:tesla, "~> 1.3", [hex: :tesla, repo: "hexpm", optional: false]}], "hexpm", "83cc6092bc3e74926d1c8455f0ce927d5d1d36707b74d9a65e38c084aab0350f"},