Add MCP example

Inspired by https://github.com/dpella/mcp/blob/main/mcp-server/example.
2026-03-19 16:59:10 +00:00 · 2026-03-19 16:59:10 +00:00 · 714ae84ed5
commit 714ae84ed5
parent da55b457ec
9 changed files with 1559 additions and 3 deletions
--- a/SKILL.md
+++ b/SKILL.md
@ -0,0 +1,202 @@
+# Example MCP Server — Build & Test Skill
+
+This skill explains how to build, run, and test the example MCP server that
+demonstrates the `mcp` Haskell library.
+
+## Prerequisites
+
+- GHC 9.12.2 and cabal-install
+- The project root is at the repository root (where `cabal.project` lives)
+
+## Build
+
+```bash
+cabal build mcp-example
+```
+
+This compiles the example server along with its dependencies (`mcp-types` and
+`mcp`).
+
+## Run
+
+```bash
+cabal run mcp-example
+```
+
+The server starts on **http://localhost:8080/mcp** and prints a JWT bearer token
+to stdout. Copy this token — you need it for all requests.
+
+## Test with curl
+
+Replace `$TOKEN` with the token printed by the server.
+
+### 1. Initialize the session
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"curl","version":"1.0"}}}'
+```
+
+### 2. Send initialized notification
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","method":"notifications/initialized","params":null}'
+```
+
+### 3. List tools
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}'
+```
+
+### 4. Call the echo tool
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"echo","arguments":{"message":"Hello from MCP!"}}}'
+```
+
+### 5. Call the add tool
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":4,"method":"tools/call","params":{"name":"add","arguments":{"a":17,"b":25}}}'
+```
+
+### 6. Call the current-time tool
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":5,"method":"tools/call","params":{"name":"current-time","arguments":{}}}'
+```
+
+### 7. List resources
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":6,"method":"resources/list","params":{}}'
+```
+
+### 8. Read a resource
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":7,"method":"resources/read","params":{"uri":"resource://example/readme"}}'
+```
+
+### 9. List resource templates
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":8,"method":"resources/templates/list","params":{}}'
+```
+
+### 10. Read a templated resource
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":9,"method":"resources/read","params":{"uri":"resource://example/users/42"}}'
+```
+
+### 11. List prompts
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":10,"method":"prompts/list","params":{}}'
+```
+
+### 12. Get a prompt
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":11,"method":"prompts/get","params":{"name":"summarize","arguments":{"text":"The MCP protocol enables AI models to interact with external tools."}}}'
+```
+
+### 13. Request completions
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":12,"method":"completion/complete","params":{"ref":{"type":"ref/prompt","name":"summarize"},"argument":{"name":"text","value":"Hel"}}}'
+```
+
+### 14. Set log level
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":13,"method":"logging/setLevel","params":{"level":"debug"}}'
+```
+
+### 15. Ping
+
+```bash
+curl -s -X POST http://localhost:8080/mcp \
+  -H 'Content-Type: application/json' \
+  -H "Authorization: Bearer $TOKEN" \
+  -d '{"jsonrpc":"2.0","id":14,"method":"ping","params":{}}'
+```
+
+## Available Features
+
+| Feature              | Methods                                      |
+|----------------------|----------------------------------------------|
+| Tools                | `tools/list`, `tools/call`                   |
+| Resources            | `resources/list`, `resources/read`           |
+| Resource Templates   | `resources/templates/list`                   |
+| Prompts              | `prompts/list`, `prompts/get`               |
+| Completions          | `completion/complete`                        |
+| Logging              | `logging/setLevel`                           |
+| Lifecycle            | `initialize`, `notifications/initialized`    |
+| Health               | `ping`                                       |
+
+## Run the agent test (Claude Agent SDK)
+
+A Node.js test in `test/` uses the Claude Agent SDK to start the server and
+exercise every tool endpoint through a Claude agent.
+
+```bash
+cd mcp-server/example/test
+pnpm install
+pnpm test   # requires ANTHROPIC_API_KEY
+```
+
+The script starts the server, captures its JWT token, connects a Claude agent,
+and verifies that all 3 tool checks pass (echo, add, current-time).
+See `test/README.md` for details.
+
+## Run the library tests
+
+```bash
+cabal test all
+```
+
+This runs the full integration test suite (42 tests) for the `mcp` library.
--- a/app/Main.hs
+++ b/app/Main.hs
@ -1,4 +1,610 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+{- | An example MCP server demonstrating the full feature set of the @mcp@ library.
+
+= Quick start
+
+@
+cabal run mcp-example                  -- HTTP with JWT auth
+cabal run mcp-example -- --simple-http -- HTTP without auth (local only)
+cabal run mcp-example -- --stdio       -- stdio transport
+@
+
+In HTTP mode (default) the server starts on @http:\/\/localhost:8080\/mcp@ and
+prints a JWT bearer token to stdout.  In simple-http mode no authentication
+is performed — use this only locally or behind an authenticating proxy.
+
+= Features demonstrated
+
+This single-file example covers every major capability of the library:
+
+* __JWT authentication__ — a fresh key is generated on startup and a sample
+  token is printed so you can test immediately.
+* __Tools__ (via 'ToolHandler' \/ 'withToolHandlers') — @echo@, @add@, and
+  @current-time@ show text results, structured output, and IO in handlers.
+* __Resources__ — static text and JSON resources served by URI.
+* __Resource templates__ — a @resource:\/\/example\/users\/{userId}@ URI template
+  that dynamically generates user profiles.
+* __Prompts__ — a @summarize@ prompt with a required @text@ argument, returning
+  a multi-message conversation.
+* __Completions__ — auto-complete suggestions for prompt argument values.
+* __Logging__ — the server declares @LoggingCapability@ and supports
+  @logging\/setLevel@.
+* __Lifecycle hooks__ — @handleInit@ and @handleFinalize@ show how to run
+  setup\/teardown logic around each session and request.
+* __Server instructions__ — a free-text string sent to clients on initialization.
+
+= Architecture overview
+
+1. Define your user type (@ExampleUser@) and per-session state (@ExampleState@).
+2. Wire them into the library via type family instances:
+   @type instance MCPHandlerState = ExampleState@ and
+   @type instance MCPHandlerUser = ExampleUser@.
+3. Build a 'ProcessHandlers' record — start from 'defaultProcessHandlers' and
+   override the capabilities you need.  Use 'withToolHandlers' for a convenient
+   tool-registration API.
+4. Create an 'MCPServerState' via 'initMCPServerState', wrap it in an 'MVar',
+   and serve it with @serveWithContext (Proxy \@MCPAPI) ctx (mcpAPI stateVar)@
+   for JWT auth, or @simpleHttpApp stateVar@ for unauthenticated local use.
+-}
 module Main where

+import Control.Concurrent.MVar (newMVar)
+import Control.Monad.IO.Class (liftIO)
+import Data.Aeson (Value, object, toJSON, (.=))
+import Data.Aeson qualified as Aeson
+import Data.ByteString.Lazy qualified as BSL
+import Data.Map.Strict qualified as Map
+import Data.Text (Text)
+import Data.Text qualified as T
+import Data.Text.Encoding qualified as TE
+import Data.Time.Clock (getCurrentTime)
+import GHC.Generics (Generic)
+import MCP.Server
+import Network.Wai.Handler.Warp qualified as Warp
+import Servant (Context (..), Proxy (..), serveWithContext)
+import Servant.Auth.Server qualified as AuthServer
+import System.Environment (getArgs, lookupEnv)
+import System.IO (hSetBuffering, stderr, stdin, stdout, BufferMode (..))
+
+-- ---------------------------------------------------------------------------
+-- User and state types
+-- ---------------------------------------------------------------------------
+
+-- | The authenticated user carried inside JWT claims.
+--
+-- The library requires instances of 'AuthServer.ToJWT' and 'AuthServer.FromJWT'
+-- so it can encode\/decode your user in bearer tokens.  Deriving 'Generic' plus
+-- 'Aeson.ToJSON' \/ 'Aeson.FromJSON' gives you those for free via the default
+-- methods.
+data ExampleUser = ExampleUser
+    { userId :: Text
+    , userName :: Text
+    }
+    deriving (Eq, Show, Generic)
+
+instance Aeson.ToJSON ExampleUser
+instance Aeson.FromJSON ExampleUser
+instance AuthServer.ToJWT ExampleUser
+instance AuthServer.FromJWT ExampleUser
+
+-- | Per-session handler state.
+--
+-- This is threaded through every 'MCPServerT' handler via 'StateT'.  You can
+-- put anything you need here — database connections, caches, etc.  For this
+-- example we just track which user is active.
+newtype ExampleState = ExampleState
+    { currentUser :: Maybe Text
+    }
+
+-- | Wire the type families so the library knows our concrete types.
+--
+-- Every application using @mcp@ must provide exactly one instance for each.
+-- @MCPHandlerState@ is the state available in handlers, and @MCPHandlerUser@
+-- is the user type decoded from JWT tokens.
+type instance MCPHandlerState = ExampleState
+type instance MCPHandlerUser = ExampleUser
+
+-- ---------------------------------------------------------------------------
+-- Tools
+-- ---------------------------------------------------------------------------
+
+-- | All tools provided by the example server.
+--
+-- We use the 'toolHandler' smart constructor for convenience — it fills in
+-- optional fields (title, output schema, annotations, metadata) with 'Nothing'.
+-- Then 'withToolHandlers' wires them into a 'ProcessHandlers' record,
+-- automatically generating the @tools\/list@ and @tools\/call@ dispatch logic.
+exampleTools :: [ToolHandler]
+exampleTools = [echoTool, addTool, currentTimeTool]
+
+-- | A simple tool that echoes its input back.
+--
+-- Demonstrates 'toolTextResult' — the simplest way to return text from a tool.
+echoTool :: ToolHandler
+echoTool =
+    toolHandler
+        "echo"
+        (Just "Echoes the input message back to the caller")
+        (InputSchema "object" (Just $ Map.fromList [("message", object ["type" .= ("string" :: Text)])]) (Just ["message"]))
+        $ \args -> do
+            let msg = args >>= Map.lookup "message" >>= asText
+            case msg of
+                Just txt -> return $ ProcessSuccess $ toolTextResult [txt]
+                Nothing -> return $ ProcessSuccess $ toolTextError "Missing or invalid 'message' argument"
+
+-- | A tool that adds two numbers.
+--
+-- Demonstrates returning structured output via 'CallToolResult' with a
+-- 'structuredContent' map alongside the human-readable text content.
+addTool :: ToolHandler
+addTool =
+    toolHandler
+        "add"
+        (Just "Adds two numbers and returns the sum")
+        ( InputSchema
+            "object"
+            ( Just $
+                Map.fromList
+                    [ ("a", object ["type" .= ("number" :: Text)])
+                    , ("b", object ["type" .= ("number" :: Text)])
+                    ]
+            )
+            (Just ["a", "b"])
+        )
+        $ \args -> do
+            let ma = args >>= Map.lookup "a" >>= asNumber
+            let mb = args >>= Map.lookup "b" >>= asNumber
+            case (ma, mb) of
+                (Just a, Just b) -> do
+                    let s = a + b
+                    return $
+                        ProcessSuccess $
+                            CallToolResult
+                                { content = [TextBlock $ TextContent "text" ("The sum is: " <> T.pack (show s)) Nothing Nothing]
+                                , structuredContent = Just $ Map.fromList [("result", toJSON s)]
+                                , isError = Just False
+                                , _meta = Nothing
+                                }
+                _ -> return $ ProcessSuccess $ toolTextError "Arguments 'a' and 'b' must be numbers"
+
+-- | A tool that returns the current UTC time.
+--
+-- Demonstrates performing IO inside a tool handler via 'liftIO'.
+currentTimeTool :: ToolHandler
+currentTimeTool =
+    toolHandler
+        "current-time"
+        (Just "Returns the current UTC time")
+        (InputSchema "object" Nothing Nothing)
+        $ \_ -> do
+            now <- liftIO getCurrentTime
+            return $ ProcessSuccess $ toolTextResult [T.pack (show now)]
+
+-- ---------------------------------------------------------------------------
+-- Resources
+-- ---------------------------------------------------------------------------
+
+-- | Static resources advertised by the server.
+--
+-- Clients discover these via @resources\/list@ and fetch their content with
+-- @resources\/read@.  Each resource has a stable URI, a human-readable name,
+-- and an optional MIME type.
+exampleResources :: [Resource]
+exampleResources =
+    [ Resource
+        { uri = "resource://example/readme"
+        , name = "readme"
+        , title = Just "Example README"
+        , description = Just "A sample text document"
+        , mimeType = Just "text/plain"
+        , size = Nothing
+        , annotations = Nothing
+        , _meta = Nothing
+        }
+    , Resource
+        { uri = "resource://example/config"
+        , name = "config"
+        , title = Just "Example Configuration"
+        , description = Just "A sample JSON configuration"
+        , mimeType = Just "application/json"
+        , size = Nothing
+        , annotations = Nothing
+        , _meta = Nothing
+        }
+    ]
+
+-- | Handle @resources\/read@ requests.
+--
+-- Routes by URI to return the appropriate content.  Unknown URIs get a 404
+-- error via 'ProcessRPCError'.  URIs matching the @resource:\/\/example\/users\/{id}@
+-- template are handled dynamically.
+readResource :: ReadResourceParams -> MCPServerT (ProcessResult ReadResourceResult)
+readResource (ReadResourceParams req_uri) =
+    case req_uri of
+        "resource://example/readme" ->
+            ok req_uri "text/plain" "This is the example MCP server README.\nIt demonstrates tools, resources, prompts, and more."
+        "resource://example/config" ->
+            ok req_uri "application/json" (T.pack $ show $ object ["version" .= ("1.0" :: Text), "debug" .= False])
+        _ ->
+            -- Handle resource template matches (see exampleResourceTemplates)
+            case T.stripPrefix "resource://example/users/" req_uri of
+                Just uid | not (T.null uid) ->
+                    ok req_uri "application/json" (T.pack $ show $ object ["userId" .= uid, "name" .= ("User " <> uid)])
+                _ -> return $ ProcessRPCError 404 "Resource not found"
+  where
+    ok u mime txt =
+        return $
+            ProcessSuccess $
+                ReadResourceResult
+                    { contents = [TextResource $ TextResourceContents u txt (Just mime) Nothing]
+                    , _meta = Nothing
+                    }
+
+-- ---------------------------------------------------------------------------
+-- Resource Templates
+-- ---------------------------------------------------------------------------
+
+-- | Resource templates advertised by the server.
+--
+-- Templates use RFC 6570 URI syntax (e.g. @{userId}@).  Clients can discover
+-- them via @resources\/templates\/list@ and then construct concrete URIs to pass
+-- to @resources\/read@.
+exampleResourceTemplates :: [ResourceTemplate]
+exampleResourceTemplates =
+    [ ResourceTemplate
+        { name = "user-profile"
+        , title = Just "User Profile"
+        , uriTemplate = "resource://example/users/{userId}"
+        , description = Just "Returns a JSON profile for a given user ID"
+        , mimeType = Just "application/json"
+        , annotations = Nothing
+        , _meta = Nothing
+        }
+    ]
+
+-- ---------------------------------------------------------------------------
+-- Prompts
+-- ---------------------------------------------------------------------------
+
+-- | Prompt templates advertised by the server.
+--
+-- Prompts are reusable conversation starters.  Each prompt declares its
+-- arguments (name, description, required flag) so clients can present a form
+-- and fill in the values before calling @prompts\/get@.
+examplePrompts :: [Prompt]
+examplePrompts =
+    [ Prompt
+        { name = "summarize"
+        , title = Just "Summarize Text"
+        , description = Just "Asks the LLM to produce a concise summary of the provided text"
+        , arguments =
+            Just
+                [ PromptArgument
+                    { name = "text"
+                    , title = Just "Text to summarize"
+                    , description = Just "The text content to summarize"
+                    , required = Just True
+                    }
+                ]
+        , _meta = Nothing
+        }
+    ]
+
+-- | Handle @prompts\/get@ requests.
+--
+-- Returns a list of 'PromptMessage' values that form a conversation.
+-- The 'User' message includes the argument value; the 'Assistant' message
+-- primes the model with a helpful starting response.
+getPrompt :: GetPromptParams -> MCPServerT (ProcessResult GetPromptResult)
+getPrompt = \case
+    GetPromptParams{name = "summarize", arguments = Just args} -> do
+        let txt = Map.findWithDefault "" "text" args
+        let msgs =
+                [ PromptMessage
+                    { role = User
+                    , content = TextBlock $ TextContent "text" ("Please summarize the following text:\n\n" <> txt) Nothing Nothing
+                    }
+                , PromptMessage
+                    { role = Assistant
+                    , content = TextBlock $ TextContent "text" "I'll provide a concise summary of the text." Nothing Nothing
+                    }
+                ]
+        return $
+            ProcessSuccess $
+                GetPromptResult
+                    { description = Just "A prompt to summarize text"
+                    , messages = msgs
+                    , _meta = Nothing
+                    }
+    _ -> return $ ProcessRPCError 404 "Prompt not found"
+
+-- ---------------------------------------------------------------------------
+-- Completions
+-- ---------------------------------------------------------------------------
+
+-- | Handle @completion\/complete@ requests.
+--
+-- Returns auto-complete suggestions for prompt argument values.  The client
+-- sends the argument name and a partial value; the server responds with
+-- matching completions.  Here we return a fixed set of suggestions for the
+-- @text@ argument of the @summarize@ prompt.
+handleComplete :: CompleteParams -> MCPServerT (ProcessResult CompleteResult)
+handleComplete (CompleteParams _ref (CompletionArgument arg_name _) _ctx) =
+    case arg_name of
+        "text" ->
+            return $
+                ProcessSuccess $
+                    CompleteResult
+                        { completion =
+                            CompletionResult
+                                { values = ["Hello world", "Lorem ipsum dolor sit amet", "The quick brown fox"]
+                                , total = Just 3
+                                , hasMore = Just False
+                                }
+                        , _meta = Nothing
+                        }
+        _ ->
+            return $
+                ProcessSuccess $
+                    CompleteResult
+                        { completion = CompletionResult{values = [], total = Just 0, hasMore = Just False}
+                        , _meta = Nothing
+                        }
+
+-- ---------------------------------------------------------------------------
+-- Process handlers
+-- ---------------------------------------------------------------------------
+
+-- | Assemble all handlers into a single 'ProcessHandlers' record.
+--
+-- Start from 'defaultProcessHandlers' (all fields 'Nothing'), override the
+-- capabilities you want, then apply 'withToolHandlers' to wire up tool
+-- listing and dispatch automatically.
+--
+-- Note that 'withToolHandlers' overwrites @listToolsHandler@ and
+-- @callToolHandler@, so it should be the outermost wrapper.
+exampleHandlers :: ProcessHandlers
+exampleHandlers =
+    withToolHandlers exampleTools $
+        defaultProcessHandlers
+            { listResourcesHandler = Just $ \_ ->
+                return $
+                    ProcessSuccess $
+                        ListResourcesResult
+                            { resources = exampleResources
+                            , nextCursor = Nothing
+                            , _meta = Nothing
+                            }
+            , readResourceHandler = Just readResource
+            , listPromptsHandler = Just $ \_ ->
+                return $
+                    ProcessSuccess $
+                        ListPromptsResult
+                            { prompts = examplePrompts
+                            , nextCursor = Nothing
+                            , _meta = Nothing
+                            }
+            , getPromptHandler = Just getPrompt
+            , listResourceTemplatesHandler = Just $ \_ ->
+                return $
+                    ProcessSuccess $
+                        ListResourceTemplatesResult
+                            { resourceTemplates = exampleResourceTemplates
+                            , nextCursor = Nothing
+                            , _meta = Nothing
+                            }
+            , completeHandler = Just handleComplete
+            }
+
+-- ---------------------------------------------------------------------------
+-- Server capabilities
+-- ---------------------------------------------------------------------------
+
+-- | Declare which MCP capabilities this server supports.
+--
+-- The client receives these during the @initialize@ handshake so it knows
+-- which methods are available.  Setting a capability to 'Nothing' means the
+-- server does not support it; setting @listChanged = Just True@ advertises
+-- that the server may send @notifications\/tools\/list_changed@ at runtime.
+exampleCapabilities :: ServerCapabilities
+exampleCapabilities =
+    ServerCapabilities
+        { logging = Just LoggingCapability
+        , prompts = Just PromptsCapability{listChanged = Nothing}
+        , resources = Just ResourcesCapability{listChanged = Nothing, subscribe = Nothing}
+        , tools = Just ToolsCapability{listChanged = Just True}
+        , completions = Just CompletionsCapability
+        , experimental = Nothing
+        }
+
+-- ---------------------------------------------------------------------------
+-- Lifecycle hooks
+-- ---------------------------------------------------------------------------
+
+-- | Called once when the client sends @initialize@.
+--
+-- Use this to set up per-session state — open database connections, load
+-- configuration, etc.  The authenticated user is provided so you can
+-- personalise the session.
+handleInit :: ExampleUser -> ExampleState -> IO ExampleState
+handleInit user st = do
+    putStrLn $ "Session initialized for user: " <> T.unpack (userId user)
+    return st{currentUser = Just (userId user)}
+
+-- | Called after every request.
+--
+-- Use this for cleanup — close cursors, flush buffers, etc.  In this example
+-- we simply clear the current user.
+handleFinalize :: ExampleState -> IO ExampleState
+handleFinalize st = return st{currentUser = Nothing}
+
+-- ---------------------------------------------------------------------------
+-- Main
+-- ---------------------------------------------------------------------------
+
+-- | Entry point.
+--
+-- Supports three modes:
+--
+-- * __HTTP mode__ (default): starts a Warp server with JWT authentication.
+-- * __Simple HTTP mode__ (@--simple-http@): starts a Warp server without
+--   authentication.  Only use locally or behind an authenticating proxy.
+-- * __Stdio mode__ (@--stdio@): reads JSON-RPC from stdin, writes to stdout.
+--   No authentication is needed.  Debug output goes to stderr.
+--
+-- @
+-- cabal run mcp-example                  # HTTP with JWT on port 8080
+-- cabal run mcp-example -- --simple-http # HTTP without auth on port 8080
+-- cabal run mcp-example -- --stdio       # stdio transport
+-- @
 main :: IO ()
-main = putStrLn "Hello, Haskell!"
+main = do
+    args <- getArgs
+    if "--stdio" `elem` args
+        then mainStdio
+        else
+            if "--simple-http" `elem` args
+                then mainSimpleHTTP
+                else mainHTTP
+
+-- | Run in stdio transport mode.
+--
+-- Reads JSON-RPC messages from stdin and writes responses to stdout.
+-- There is no JWT authentication — the caller is trusted.
+-- Debug/log output goes to stderr so it doesn't interfere with the protocol.
+mainStdio :: IO ()
+mainStdio = do
+    hSetBuffering stderr LineBuffering
+
+    let impl = Implementation "mcp-example" "0.1.0" (Just "Example MCP Server")
+    let server_instructions = Just "This is an example MCP server. It provides echo, add, and current-time tools, sample resources, a summarize prompt, and completions."
+    let initial_state =
+            (initMCPServerState
+                (ExampleState Nothing) -- initial handler state
+                Nothing -- no handler init in stdio mode (no JWT user)
+                (Just handleFinalize) -- lifecycle: after each request
+                exampleCapabilities -- what we support
+                impl -- server name + version
+                server_instructions -- instructions for clients
+                exampleHandlers -- all our handlers
+            ){mcp_log_level = Just Debug}
+
+    serveStdio stdin stdout initial_state
+
+-- | Run in simple HTTP mode without authentication.
+--
+-- No JWT or servant-auth.  This transport should only be used locally or
+-- behind a reverse proxy that handles authentication.
+--
+-- @
+-- cabal run mcp-example -- --simple-http
+-- @
+mainSimpleHTTP :: IO ()
+mainSimpleHTTP = do
+    hSetBuffering stdout LineBuffering
+
+    port <- maybe 8080 read <$> lookupEnv "PORT"
+
+    let impl = Implementation "mcp-example" "0.1.0" (Just "Example MCP Server (SimpleHTTP)")
+    let server_instructions = Just "This is an example MCP server using the SimpleHTTP transport. It provides echo, add, and current-time tools, sample resources, a summarize prompt, and completions."
+
+    let initial_state =
+            (initMCPServerState
+                (ExampleState Nothing) -- initial handler state
+                Nothing -- no handler init (no user type in SimpleHTTP)
+                (Just handleFinalize) -- lifecycle: after each request
+                exampleCapabilities -- what we support
+                impl -- server name + version
+                server_instructions -- instructions for clients
+                exampleHandlers -- all our handlers
+            ){mcp_log_level = Just Debug}
+    state_var <- newMVar initial_state
+
+    putStrLn "=== Example MCP Server (SimpleHTTP) ==="
+    putStrLn $ "Listening on http://localhost:" <> show port <> "/mcp"
+    putStrLn "WARNING: No authentication — only use locally or behind an authenticating proxy."
+    putStrLn ""
+    putStrLn "Example curl:"
+    putStrLn $ "  curl -X POST http://localhost:" <> show port <> "/mcp \\"
+    putStrLn "    -H 'Content-Type: application/json' \\"
+    putStrLn "    -d '{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\",\"params\":{\"protocolVersion\":\"2025-06-18\",\"capabilities\":{},\"clientInfo\":{\"name\":\"curl\",\"version\":\"1.0\"}}}'"
+
+    let app = simpleHttpApp state_var
+    Warp.run port app
+
+-- | Run in HTTP mode with JWT authentication.
+mainHTTP :: IO ()
+mainHTTP = do
+    -- Use line buffering so output is visible immediately when piped.
+    hSetBuffering stdout LineBuffering
+
+    -- Read port from PORT env var, default to 8080.
+    port <- maybe 8080 read <$> lookupEnv "PORT"
+
+    -- Server metadata shown to clients during initialization.
+    let impl = Implementation "mcp-example" "0.1.0" (Just "Example MCP Server")
+
+    -- Free-text instructions sent to clients on initialization.
+    let server_instructions = Just "This is an example MCP server. It provides echo, add, and current-time tools, sample resources, a summarize prompt, and completions."
+
+    -- Create the initial server state.  initMCPServerState sets sensible
+    -- defaults: not yet initialized, log level Warning, empty pending responses.
+    -- We override the log level to Debug so all requests/responses are logged.
+    let initial_state =
+            (initMCPServerState
+                (ExampleState Nothing) -- initial handler state
+                (Just handleInit) -- lifecycle: on initialize
+                (Just handleFinalize) -- lifecycle: after each request
+                exampleCapabilities -- what we support
+                impl -- server name + version
+                server_instructions -- instructions for clients
+                exampleHandlers -- all our handlers
+            ){mcp_log_level = Just Debug}
+    state_var <- newMVar initial_state
+
+    -- Generate a fresh JWK key for signing tokens.
+    key <- AuthServer.generateKey
+    let jwt_cfg = AuthServer.defaultJWTSettings key
+    let cookie_cfg = AuthServer.defaultCookieSettings
+    -- The Servant context carries the auth configuration used by servant-auth.
+    let ctx = cookie_cfg :. jwt_cfg :. EmptyContext
+
+    -- Mint a JWT for a test user so you can start making requests immediately.
+    let test_user = ExampleUser "example-user" "Example User"
+    token_result <- AuthServer.makeJWT test_user jwt_cfg Nothing
+    case token_result of
+        Left err -> putStrLn $ "Failed to generate JWT: " <> show err
+        Right token -> do
+            let token_str = TE.decodeUtf8 $ BSL.toStrict token
+            putStrLn "=== Example MCP Server ==="
+            putStrLn $ "Listening on http://localhost:" <> show port <> "/mcp"
+            putStrLn ""
+            putStrLn "Bearer token for testing:"
+            putStrLn $ T.unpack token_str
+            putStrLn ""
+            putStrLn "Example curl:"
+            putStrLn $ "  curl -X POST http://localhost:" <> show port <> "/mcp \\"
+            putStrLn "    -H 'Content-Type: application/json' \\"
+            putStrLn $ "    -H 'Authorization: Bearer " <> T.unpack token_str <> "' \\"
+            putStrLn "    -d '{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\",\"params\":{\"protocolVersion\":\"2025-06-18\",\"capabilities\":{},\"clientInfo\":{\"name\":\"curl\",\"version\":\"1.0\"}}}'"
+
+    -- Build the Servant application and start Warp.
+    let app = serveWithContext (Proxy @MCPAPI) ctx (mcpAPI state_var)
+    Warp.run port app
+
+-- ---------------------------------------------------------------------------
+-- JSON value helpers
+-- ---------------------------------------------------------------------------
+
+-- | Extract a 'Text' from a JSON 'Value', returning 'Nothing' for non-strings.
+asText :: Value -> Maybe Text
+asText (Aeson.String t) = Just t
+asText _ = Nothing
+
+-- | Extract a 'Double' from a JSON 'Value', returning 'Nothing' for non-numbers.
+asNumber :: Value -> Maybe Double
+asNumber (Aeson.Number n) = Just (realToFrac n)
+asNumber _ = Nothing
--- a/cabal.project
+++ b/cabal.project
@ -1,4 +1,5 @@
 packages: .

+-- https://github.com/frasertweedale/hs-jose/pull/137#issuecomment-4090951037
 constraints:
  crypton == 1.0.7,
--- a/mcp-config.json
+++ b/mcp-config.json
@ -0,0 +1,11 @@
+{
+  "mcpServers": {
+    "mcp-example": {
+      "url": "http://localhost:8080/mcp",
+      "headers": {
+        "Authorization": "Bearer <PASTE_TOKEN_FROM_SERVER_OUTPUT>"
+      },
+      "description": "Example MCP server demonstrating tools, resources, prompts, and completions. Start the server first with: cabal run mcp-example"
+    }
+  }
+}
--- a/mcp-example.cabal
+++ b/mcp-example.cabal
@ -1,16 +1,20 @@
 cabal-version: 3.0
-name: hello-hs
+name: mcp-example
 version: 0.1.0.0
 license-file: LICENSE
 author: George Thomas
 maintainer: georgefsthomas@gmail.com

-executable hello-hs
+executable mcp-example
    main-is: Main.hs
    hs-source-dirs: app
    default-language: GHC2021
+    default-extensions:
+        DuplicateRecordFields
+        LambdaCase
    ghc-options:
        -Wall
+        -threaded
    build-depends:
        base,
        aeson,
@ -29,3 +33,4 @@ executable hello-hs
        time,
        transformers,
        wai,
+        warp,
--- a/test/.gitignore
+++ b/test/.gitignore
@ -0,0 +1 @@
+node_modules/
--- a/test/package.json
+++ b/test/package.json
@ -0,0 +1,12 @@
+{
+  "name": "mcp-example-test",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "test": "node test_mcp_server.mjs"
+  },
+  "dependencies": {
+    "@anthropic-ai/claude-agent-sdk": "^0.2.42"
+  }
+}
--- a/test/pnpm-lock.yaml
+++ b/test/pnpm-lock.yaml
@ -0,0 +1,193 @@
+lockfileVersion: '9.0'
+
+settings:
+  autoInstallPeers: true
+  excludeLinksFromLockfile: false
+
+importers:
+
+  .:
+    dependencies:
+      '@anthropic-ai/claude-agent-sdk':
+        specifier: ^0.2.42
+        version: 0.2.42(zod@4.3.6)
+
+packages:
+
+  '@anthropic-ai/claude-agent-sdk@0.2.42':
+    resolution: {integrity: sha512-/CugP7AjP57Dqtl2sbsDtxdbpQoPKIhjyF5WrTViGu4NHQdM+UikrRs4MhZ2jeotiC5R7iK9ZUN9SiBgcZ8oLw==}
+    engines: {node: '>=18.0.0'}
+    peerDependencies:
+      zod: ^4.0.0
+
+  '@img/sharp-darwin-arm64@0.33.5':
+    resolution: {integrity: sha512-UT4p+iz/2H4twwAoLCqfA9UH5pI6DggwKEGuaPy7nCVQ8ZsiY5PIcrRvD1DzuY3qYL07NtIQcWnBSY/heikIFQ==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [arm64]
+    os: [darwin]
+
+  '@img/sharp-darwin-x64@0.33.5':
+    resolution: {integrity: sha512-fyHac4jIc1ANYGRDxtiqelIbdWkIuQaI84Mv45KvGRRxSAa7o7d1ZKAOBaYbnepLC1WqxfpimdeWfvqqSGwR2Q==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [x64]
+    os: [darwin]
+
+  '@img/sharp-libvips-darwin-arm64@1.0.4':
+    resolution: {integrity: sha512-XblONe153h0O2zuFfTAbQYAX2JhYmDHeWikp1LM9Hul9gVPjFY427k6dFEcOL72O01QxQsWi761svJ/ev9xEDg==}
+    cpu: [arm64]
+    os: [darwin]
+
+  '@img/sharp-libvips-darwin-x64@1.0.4':
+    resolution: {integrity: sha512-xnGR8YuZYfJGmWPvmlunFaWJsb9T/AO2ykoP3Fz/0X5XV2aoYBPkX6xqCQvUTKKiLddarLaxpzNe+b1hjeWHAQ==}
+    cpu: [x64]
+    os: [darwin]
+
+  '@img/sharp-libvips-linux-arm64@1.0.4':
+    resolution: {integrity: sha512-9B+taZ8DlyyqzZQnoeIvDVR/2F4EbMepXMc/NdVbkzsJbzkUjhXv/70GQJ7tdLA4YJgNP25zukcxpX2/SueNrA==}
+    cpu: [arm64]
+    os: [linux]
+    libc: [glibc]
+
+  '@img/sharp-libvips-linux-arm@1.0.5':
+    resolution: {integrity: sha512-gvcC4ACAOPRNATg/ov8/MnbxFDJqf/pDePbBnuBDcjsI8PssmjoKMAz4LtLaVi+OnSb5FK/yIOamqDwGmXW32g==}
+    cpu: [arm]
+    os: [linux]
+    libc: [glibc]
+
+  '@img/sharp-libvips-linux-x64@1.0.4':
+    resolution: {integrity: sha512-MmWmQ3iPFZr0Iev+BAgVMb3ZyC4KeFc3jFxnNbEPas60e1cIfevbtuyf9nDGIzOaW9PdnDciJm+wFFaTlj5xYw==}
+    cpu: [x64]
+    os: [linux]
+    libc: [glibc]
+
+  '@img/sharp-libvips-linuxmusl-arm64@1.0.4':
+    resolution: {integrity: sha512-9Ti+BbTYDcsbp4wfYib8Ctm1ilkugkA/uscUn6UXK1ldpC1JjiXbLfFZtRlBhjPZ5o1NCLiDbg8fhUPKStHoTA==}
+    cpu: [arm64]
+    os: [linux]
+    libc: [musl]
+
+  '@img/sharp-libvips-linuxmusl-x64@1.0.4':
+    resolution: {integrity: sha512-viYN1KX9m+/hGkJtvYYp+CCLgnJXwiQB39damAO7WMdKWlIhmYTfHjwSbQeUK/20vY154mwezd9HflVFM1wVSw==}
+    cpu: [x64]
+    os: [linux]
+    libc: [musl]
+
+  '@img/sharp-linux-arm64@0.33.5':
+    resolution: {integrity: sha512-JMVv+AMRyGOHtO1RFBiJy/MBsgz0x4AWrT6QoEVVTyh1E39TrCUpTRI7mx9VksGX4awWASxqCYLCV4wBZHAYxA==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [glibc]
+
+  '@img/sharp-linux-arm@0.33.5':
+    resolution: {integrity: sha512-JTS1eldqZbJxjvKaAkxhZmBqPRGmxgu+qFKSInv8moZ2AmT5Yib3EQ1c6gp493HvrvV8QgdOXdyaIBrhvFhBMQ==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [arm]
+    os: [linux]
+    libc: [glibc]
+
+  '@img/sharp-linux-x64@0.33.5':
+    resolution: {integrity: sha512-opC+Ok5pRNAzuvq1AG0ar+1owsu842/Ab+4qvU879ippJBHvyY5n2mxF1izXqkPYlGuP/M556uh53jRLJmzTWA==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [glibc]
+
+  '@img/sharp-linuxmusl-arm64@0.33.5':
+    resolution: {integrity: sha512-XrHMZwGQGvJg2V/oRSUfSAfjfPxO+4DkiRh6p2AFjLQztWUuY/o8Mq0eMQVIY7HJ1CDQUJlxGGZRw1a5bqmd1g==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [musl]
+
+  '@img/sharp-linuxmusl-x64@0.33.5':
+    resolution: {integrity: sha512-WT+d/cgqKkkKySYmqoZ8y3pxx7lx9vVejxW/W4DOFMYVSkErR+w7mf2u8m/y4+xHe7yY9DAXQMWQhpnMuFfScw==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [musl]
+
+  '@img/sharp-win32-x64@0.33.5':
+    resolution: {integrity: sha512-MpY/o8/8kj+EcnxwvrP4aTJSWw/aZ7JIGR4aBeZkZw5B7/Jn+tY9/VNwtcoGmdT7GfggGIU4kygOMSbYnOrAbg==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [x64]
+    os: [win32]
+
+  zod@4.3.6:
+    resolution: {integrity: sha512-rftlrkhHZOcjDwkGlnUtZZkvaPHCsDATp4pGpuOOMDaTdDDXF91wuVDJoWoPsKX/3YPQ5fHuF3STjcYyKr+Qhg==}
+
+snapshots:
+
+  '@anthropic-ai/claude-agent-sdk@0.2.42(zod@4.3.6)':
+    dependencies:
+      zod: 4.3.6
+    optionalDependencies:
+      '@img/sharp-darwin-arm64': 0.33.5
+      '@img/sharp-darwin-x64': 0.33.5
+      '@img/sharp-linux-arm': 0.33.5
+      '@img/sharp-linux-arm64': 0.33.5
+      '@img/sharp-linux-x64': 0.33.5
+      '@img/sharp-linuxmusl-arm64': 0.33.5
+      '@img/sharp-linuxmusl-x64': 0.33.5
+      '@img/sharp-win32-x64': 0.33.5
+
+  '@img/sharp-darwin-arm64@0.33.5':
+    optionalDependencies:
+      '@img/sharp-libvips-darwin-arm64': 1.0.4
+    optional: true
+
+  '@img/sharp-darwin-x64@0.33.5':
+    optionalDependencies:
+      '@img/sharp-libvips-darwin-x64': 1.0.4
+    optional: true
+
+  '@img/sharp-libvips-darwin-arm64@1.0.4':
+    optional: true
+
+  '@img/sharp-libvips-darwin-x64@1.0.4':
+    optional: true
+
+  '@img/sharp-libvips-linux-arm64@1.0.4':
+    optional: true
+
+  '@img/sharp-libvips-linux-arm@1.0.5':
+    optional: true
+
+  '@img/sharp-libvips-linux-x64@1.0.4':
+    optional: true
+
+  '@img/sharp-libvips-linuxmusl-arm64@1.0.4':
+    optional: true
+
+  '@img/sharp-libvips-linuxmusl-x64@1.0.4':
+    optional: true
+
+  '@img/sharp-linux-arm64@0.33.5':
+    optionalDependencies:
+      '@img/sharp-libvips-linux-arm64': 1.0.4
+    optional: true
+
+  '@img/sharp-linux-arm@0.33.5':
+    optionalDependencies:
+      '@img/sharp-libvips-linux-arm': 1.0.5
+    optional: true
+
+  '@img/sharp-linux-x64@0.33.5':
+    optionalDependencies:
+      '@img/sharp-libvips-linux-x64': 1.0.4
+    optional: true
+
+  '@img/sharp-linuxmusl-arm64@0.33.5':
+    optionalDependencies:
+      '@img/sharp-libvips-linuxmusl-arm64': 1.0.4
+    optional: true
+
+  '@img/sharp-linuxmusl-x64@0.33.5':
+    optionalDependencies:
+      '@img/sharp-libvips-linuxmusl-x64': 1.0.4
+    optional: true
+
+  '@img/sharp-win32-x64@0.33.5':
+    optional: true
+
+  zod@4.3.6: {}
--- a/test/test_mcp_server.mjs
+++ b/test/test_mcp_server.mjs
@ -0,0 +1,525 @@
+#!/usr/bin/env node
+/**
+ * Test the example MCP server using the Claude Agent SDK.
+ *
+ * Builds the example server once, then exercises every tool endpoint
+ * over HTTP (JWT), simple HTTP (unauthenticated), and stdio transports.
+ *
+ * Usage:
+ *   # From the repository root:
+ *   cabal build mcp-example
+ *   cd mcp-server/example/test
+ *   npm install
+ *   npm test
+ *
+ * Requires:
+ *   - ANTHROPIC_API_KEY environment variable set
+ *   - GHC 9.12 + cabal (to build the server)
+ */
+
+import { query } from "@anthropic-ai/claude-agent-sdk";
+import { execSync, spawn } from "node:child_process";
+import { createServer } from "node:net";
+import { existsSync } from "node:fs";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+import http from "node:http";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+// ---------------------------------------------------------------------------
+// Server management
+// ---------------------------------------------------------------------------
+
+function findRepoRoot() {
+  let d = __dirname;
+  for (let i = 0; i < 10; i++) {
+    if (existsSync(join(d, "cabal.project"))) return d;
+    d = dirname(d);
+  }
+  return null;
+}
+
+function buildServer(repoRoot) {
+  console.log("  Building mcp-example (this may take a while)...");
+  execSync("cabal build mcp-example", { cwd: repoRoot, stdio: "inherit" });
+  console.log("  Build succeeded.");
+}
+
+function getServerBin(repoRoot) {
+  return execSync("cabal list-bin mcp-example", {
+    cwd: repoRoot,
+    encoding: "utf-8",
+  }).trim();
+}
+
+function getFreePort() {
+  return new Promise((resolve, reject) => {
+    const srv = createServer();
+    srv.listen(0, () => {
+      const { port } = srv.address();
+      srv.close(() => resolve(port));
+    });
+    srv.on("error", reject);
+  });
+}
+
+function startServer(repoRoot, port) {
+  return new Promise((resolve, reject) => {
+    console.log(`  repo root: ${repoRoot}`);
+    console.log(`  port:      ${port}`);
+    const serverBin = getServerBin(repoRoot);
+    console.log(`  binary:    ${serverBin}`);
+
+    const proc = spawn(serverBin, [], {
+      cwd: repoRoot,
+      stdio: ["ignore", "pipe", "pipe"],
+      env: { ...process.env, PORT: String(port) },
+    });
+
+    proc.stderr.on("data", (chunk) => {
+      for (const line of chunk.toString().split("\n").filter(Boolean)) {
+        console.log(`  [server:stderr] ${line}`);
+      }
+    });
+
+    let token = null;
+    const deadline = Date.now() + 30_000;
+    console.log("  Waiting for server to print JWT token...");
+
+    let buf = "";
+    proc.stdout.on("data", (chunk) => {
+      buf += chunk.toString();
+      const lines = buf.split("\n");
+      buf = lines.pop(); // keep incomplete trailing line
+      for (const raw of lines) {
+        const line = raw.trim();
+        console.log(`  [server:stdout] ${line}`);
+        if (!token && line.startsWith("eyJ")) {
+          token = line;
+        }
+      }
+    });
+
+    const check = setInterval(() => {
+      if (token) {
+        clearInterval(check);
+        // Give the server a moment to finish binding.
+        setTimeout(() => verifyAndResolve(), 1000);
+      } else if (Date.now() > deadline) {
+        clearInterval(check);
+        proc.kill();
+        reject(new Error("Timed out waiting for JWT token"));
+      }
+    }, 200);
+
+    function verifyAndResolve() {
+      console.log("  Verifying server is reachable...");
+      const body = JSON.stringify({
+        jsonrpc: "2.0",
+        id: 1,
+        method: "ping",
+      });
+      const req = http.request(
+        {
+          hostname: "localhost",
+          port,
+          path: "/mcp",
+          method: "POST",
+          headers: {
+            "Content-Type": "application/json",
+            Authorization: `Bearer ${token}`,
+          },
+        },
+        (res) => {
+          let data = "";
+          res.on("data", (c) => (data += c));
+          res.on("end", () => {
+            console.log(`  Server responded: ${data.slice(0, 200)}`);
+            resolve({ proc, token });
+          });
+        },
+      );
+      req.on("error", (e) => {
+        proc.kill();
+        reject(new Error(`Server not reachable on port ${port}: ${e.message}`));
+      });
+      req.end(body);
+    }
+
+    proc.on("error", (err) => {
+      clearInterval(check);
+      reject(err);
+    });
+    proc.on("exit", (code) => {
+      if (!token) {
+        clearInterval(check);
+        reject(new Error(`Server exited with code ${code} before printing token`));
+      }
+    });
+  });
+}
+
+function startSimpleHTTPServer(repoRoot, port) {
+  return new Promise((resolve, reject) => {
+    console.log(`  repo root: ${repoRoot}`);
+    console.log(`  port:      ${port}`);
+    const serverBin = getServerBin(repoRoot);
+    console.log(`  binary:    ${serverBin}`);
+
+    const proc = spawn(serverBin, ["--simple-http"], {
+      cwd: repoRoot,
+      stdio: ["ignore", "pipe", "pipe"],
+      env: { ...process.env, PORT: String(port) },
+    });
+
+    proc.stderr.on("data", (chunk) => {
+      for (const line of chunk.toString().split("\n").filter(Boolean)) {
+        console.log(`  [server:stderr] ${line}`);
+      }
+    });
+
+    let ready = false;
+    const deadline = Date.now() + 30_000;
+    console.log("  Waiting for simple HTTP server to start...");
+
+    let buf = "";
+    proc.stdout.on("data", (chunk) => {
+      buf += chunk.toString();
+      const lines = buf.split("\n");
+      buf = lines.pop(); // keep incomplete trailing line
+      for (const raw of lines) {
+        const line = raw.trim();
+        console.log(`  [server:stdout] ${line}`);
+        if (!ready && line.includes("Listening on")) {
+          ready = true;
+        }
+      }
+    });
+
+    const check = setInterval(() => {
+      if (ready) {
+        clearInterval(check);
+        // Give the server a moment to finish binding.
+        setTimeout(() => verifyAndResolve(), 1000);
+      } else if (Date.now() > deadline) {
+        clearInterval(check);
+        proc.kill();
+        reject(new Error("Timed out waiting for simple HTTP server"));
+      }
+    }, 200);
+
+    function verifyAndResolve() {
+      console.log("  Verifying server is reachable...");
+      const body = JSON.stringify({
+        jsonrpc: "2.0",
+        id: 1,
+        method: "ping",
+      });
+      const req = http.request(
+        {
+          hostname: "localhost",
+          port,
+          path: "/mcp",
+          method: "POST",
+          headers: {
+            "Content-Type": "application/json",
+          },
+        },
+        (res) => {
+          let data = "";
+          res.on("data", (c) => (data += c));
+          res.on("end", () => {
+            console.log(`  Server responded: ${data.slice(0, 200)}`);
+            resolve({ proc });
+          });
+        },
+      );
+      req.on("error", (e) => {
+        proc.kill();
+        reject(new Error(`Server not reachable on port ${port}: ${e.message}`));
+      });
+      req.end(body);
+    }
+
+    proc.on("error", (err) => {
+      clearInterval(check);
+      reject(err);
+    });
+    proc.on("exit", (code) => {
+      if (!ready) {
+        clearInterval(check);
+        reject(new Error(`Server exited with code ${code} before becoming ready`));
+      }
+    });
+  });
+}
+
+function stopServer(proc) {
+  proc.kill("SIGTERM");
+  setTimeout(() => proc.kill("SIGKILL"), 5000);
+}
+
+// ---------------------------------------------------------------------------
+// Agent runner
+// ---------------------------------------------------------------------------
+
+const TEST_PROMPT = `\
+You MUST call these MCP tools directly as tool calls (do NOT use Bash or any other tool):
+
+1. Call mcp__mcp-example__echo with {"message": "Hello MCP!"} — report the returned text.
+2. Call mcp__mcp-example__add with {"a": 17, "b": 25} — report the numeric result.
+3. Call mcp__mcp-example__current-time with {} — report the returned time string.
+
+After all three tool calls, print "ALL TESTS DONE".
+`;
+
+const AGENT_TIMEOUT_MS = 120_000;
+
+async function runAgent(mcpServers) {
+  const fullText = [];
+
+  console.log("  Starting agent (connecting to MCP server + API)...");
+
+  const controller = new AbortController();
+  const timer = setTimeout(() => {
+    console.log(`  ERROR: Agent timed out after ${AGENT_TIMEOUT_MS / 1000}s`);
+    controller.abort();
+  }, AGENT_TIMEOUT_MS);
+
+  try {
+    for await (const message of query({
+      prompt: TEST_PROMPT,
+      options: {
+        mcpServers,
+        allowedTools: ["mcp__mcp-example__*"],
+        disallowedTools: [
+          "Bash",
+          "Read",
+          "Edit",
+          "Write",
+          "Glob",
+          "Grep",
+          "WebFetch",
+          "WebSearch",
+          "NotebookEdit",
+          "TodoWrite",
+          "Task",
+        ],
+        permissionMode: "bypassPermissions",
+        allowDangerouslySkipPermissions: true,
+        maxTurns: 10,
+        settingSources: [],
+        abortController: controller,
+      },
+    })) {
+      if (message.type === "system" && message.subtype === "init") {
+        console.log(
+          `  [system:init] model=${message.model} tools=${JSON.stringify(message.tools)} mcp=${JSON.stringify(message.mcp_servers)}`,
+        );
+      } else if (message.type === "assistant") {
+        for (const block of message.message.content) {
+          if ("text" in block) {
+            console.log(`  [assistant] ${block.text.slice(0, 200)}`);
+            fullText.push(block.text);
+          } else if ("name" in block) {
+            console.log(
+              `  [tool_use] ${block.name}(${JSON.stringify(block.input).slice(0, 200)})`,
+            );
+          }
+        }
+      } else if (message.type === "user") {
+        const content = message.message?.content;
+        if (Array.isArray(content)) {
+          for (const block of content) {
+            if (block.type === "tool_result") {
+              const text =
+                typeof block.content === "string"
+                  ? block.content
+                  : JSON.stringify(block.content);
+              console.log(`  [tool_result] ${text?.slice(0, 200)}`);
+              if (text) fullText.push(text);
+            }
+          }
+        }
+      } else if (message.type === "result") {
+        console.log(
+          `  [result] subtype=${message.subtype} turns=${message.num_turns} cost=$${message.total_cost_usd}`,
+        );
+        if (message.subtype !== "success") {
+          console.log(`  [result] errors: ${message.errors}`);
+        }
+      }
+    }
+  } catch (err) {
+    if (err.name === "AbortError") {
+      console.log("  Agent aborted (timeout).");
+    } else {
+      console.log(`  ERROR in query(): ${err.message}`);
+    }
+  } finally {
+    clearTimeout(timer);
+  }
+
+  return fullText.join("\n");
+}
+
+// ---------------------------------------------------------------------------
+// Result checking
+// ---------------------------------------------------------------------------
+
+const CHECKS = [
+  ["echo tool", (t) => t.includes("Hello MCP!")],
+  ["add tool", (t) => t.includes("42")],
+  ["current-time tool", (t) => /\d{4}-\d{2}-\d{2}/.test(t)],
+];
+
+function evaluate(output) {
+  let passed = 0;
+  let failed = 0;
+  for (const [name, check] of CHECKS) {
+    if (check(output)) {
+      console.log(`  PASS: ${name}`);
+      passed++;
+    } else {
+      console.log(`  FAIL: ${name}`);
+      failed++;
+    }
+  }
+  return { passed, failed };
+}
+
+// ---------------------------------------------------------------------------
+// Transport tests
+// ---------------------------------------------------------------------------
+
+async function testHTTP(repoRoot) {
+  const port = await getFreePort();
+  console.log(`Starting MCP example server on port ${port}...`);
+  const { proc, token } = await startServer(repoRoot, port);
+  console.log(`Server started (token: ${token.slice(0, 20)}...)`);
+
+  try {
+    console.log("\nRunning HTTP agent tests...");
+    const output = await runAgent({
+      "mcp-example": {
+        type: "http",
+        url: `http://localhost:${port}/mcp`,
+        headers: {
+          Authorization: `Bearer ${token}`,
+        },
+      },
+    });
+
+    console.log("\n--- HTTP agent output ---");
+    console.log(output);
+    console.log("--- End HTTP agent output ---\n");
+
+    console.log("HTTP results:");
+    return evaluate(output);
+  } finally {
+    console.log("\nStopping HTTP server...");
+    stopServer(proc);
+  }
+}
+
+async function testSimpleHTTP(repoRoot) {
+  const port = await getFreePort();
+  console.log(`Starting simple HTTP MCP server on port ${port}...`);
+  const { proc } = await startSimpleHTTPServer(repoRoot, port);
+  console.log("Server started (no auth).");
+
+  try {
+    console.log("\nRunning simple HTTP agent tests...");
+    const output = await runAgent({
+      "mcp-example": {
+        type: "http",
+        url: `http://localhost:${port}/mcp`,
+      },
+    });
+
+    console.log("\n--- Simple HTTP agent output ---");
+    console.log(output);
+    console.log("--- End simple HTTP agent output ---\n");
+
+    console.log("Simple HTTP results:");
+    return evaluate(output);
+  } finally {
+    console.log("\nStopping simple HTTP server...");
+    stopServer(proc);
+  }
+}
+
+async function testStdio(serverBin) {
+  console.log("\nRunning stdio agent tests...");
+  console.log(`  binary: ${serverBin}`);
+
+  const output = await runAgent({
+    "mcp-example": {
+      type: "stdio",
+      command: serverBin,
+      args: ["--stdio"],
+    },
+  });
+
+  console.log("\n--- Stdio agent output ---");
+  console.log(output);
+  console.log("--- End stdio agent output ---\n");
+
+  console.log("Stdio results:");
+  return evaluate(output);
+}
+
+// ---------------------------------------------------------------------------
+// Main
+// ---------------------------------------------------------------------------
+
+async function main() {
+  if (!process.env.ANTHROPIC_API_KEY) {
+    console.error("Error: ANTHROPIC_API_KEY environment variable not set");
+    process.exit(1);
+  }
+
+  const repoRoot = findRepoRoot();
+  if (!repoRoot) {
+    console.error("Error: could not find repository root (cabal.project)");
+    process.exit(1);
+  }
+
+  // Build once, reuse for all transports.
+  buildServer(repoRoot);
+  const serverBin = getServerBin(repoRoot);
+
+  let totalPassed = 0;
+  let totalFailed = 0;
+
+  // --- HTTP ---
+  {
+    const { passed, failed } = await testHTTP(repoRoot);
+    totalPassed += passed;
+    totalFailed += failed;
+  }
+
+  // --- Simple HTTP ---
+  {
+    const { passed, failed } = await testSimpleHTTP(repoRoot);
+    totalPassed += passed;
+    totalFailed += failed;
+  }
+
+  // --- Stdio ---
+  {
+    const { passed, failed } = await testStdio(serverBin);
+    totalPassed += passed;
+    totalFailed += failed;
+  }
+
+  console.log(`\nOverall: ${totalPassed}/${totalPassed + totalFailed} checks passed`);
+  if (totalFailed > 0) process.exit(1);
+  console.log("Done.");
+}
+
+main().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});