From f6ebefe238cc052694a9d51ec9703b3d0c2fc576 Mon Sep 17 00:00:00 2001
From: Olivier Chafik <ochafik@anthropic.com>
Date: Mon, 8 Dec 2025 18:45:50 +0100
Subject: [PATCH] Add server selector to basic-host example (#95)
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* Add server selector to basic-host example

- Add ServerSelector component to switch between MCP servers
- Run all example servers concurrently on ports 3101-3107
- Update examples:start to launch all servers with assigned ports

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Move server selector into tool call panel

- Server selector now in same component as tool selector
- Tool call results persist across server switches
- Connection caching avoids reconnects when switching servers
- Display server name with tool name in results (ServerName:ToolName)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>
---
 examples/basic-host/src/index.module.css |   9 ++
 examples/basic-host/src/index.tsx        | 167 ++++++++++++++++-------
 package.json                             |  11 +-
 3 files changed, 138 insertions(+), 49 deletions(-)

diff --git a/examples/basic-host/src/index.module.css b/examples/basic-host/src/index.module.css
index bbaa542..961d078 100644
--- a/examples/basic-host/src/index.module.css
+++ b/examples/basic-host/src/index.module.css
@@ -1,3 +1,9 @@
+.connecting {
+  padding: 1rem 0;
+  text-align: center;
+  color: #666;
+}
+
 .callToolPanel, .toolCallInfoPanel {
   margin: 0 auto;
   padding: 1rem;
@@ -10,6 +16,9 @@
 }
 
 .callToolPanel {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
   max-width: 480px;
 
   form {
diff --git a/examples/basic-host/src/index.tsx b/examples/basic-host/src/index.tsx
index 26df1ff..1db4d29 100644
--- a/examples/basic-host/src/index.tsx
+++ b/examples/basic-host/src/index.tsx
@@ -4,35 +4,113 @@ import { callTool, connectToServer, hasAppHtml, initializeApp, loadSandboxProxy,
 import styles from "./index.module.css";
 
 
-const MCP_SERVER_URL = new URL("http://localhost:3001/mcp");
+// Available MCP servers - using ports 3101+ to avoid conflicts with common dev ports
+const SERVERS = [
+  { name: "Basic React", port: 3101 },
+  { name: "Vanilla JS", port: 3102 },
+  { name: "Budget Allocator", port: 3103 },
+  { name: "Cohort Heatmap", port: 3104 },
+  { name: "Customer Segmentation", port: 3105 },
+  { name: "Scenario Modeler", port: 3106 },
+  { name: "System Monitor", port: 3107 },
+] as const;
 
-
-interface HostProps {
-  serverInfoPromise: Promise<ServerInfo>;
+function serverUrl(port: number): string {
+  return `http://localhost:${port}/mcp`;
 }
-function Host({ serverInfoPromise }: HostProps) {
-  const serverInfo = use(serverInfoPromise);
-  const [toolCallInfos, setToolCallInfos] = useState<ToolCallInfo[]>([]);
+
+// Cache server connections to avoid reconnecting when switching between servers
+const serverInfoCache = new Map<number, Promise<ServerInfo>>();
+
+function getServerInfo(port: number): Promise<ServerInfo> {
+  let promise = serverInfoCache.get(port);
+  if (!promise) {
+    promise = connectToServer(new URL(serverUrl(port)));
+    // Remove from cache on failure so retry is possible
+    promise.catch(() => serverInfoCache.delete(port));
+    serverInfoCache.set(port, promise);
+  }
+  return promise;
+}
+
+
+// Wrapper to track server name with each tool call
+interface ToolCallEntry {
+  serverName: string;
+  info: ToolCallInfo;
+}
+
+// Host just manages tool call results - no server dependency
+function Host() {
+  const [toolCalls, setToolCalls] = useState<ToolCallEntry[]>([]);
 
   return (
     <>
-      {toolCallInfos.map((info, i) => (
-        <ToolCallInfoPanel key={i} toolCallInfo={info} />
+      {toolCalls.map((entry, i) => (
+        <ToolCallInfoPanel key={i} serverName={entry.serverName} toolCallInfo={entry.info} />
       ))}
       <CallToolPanel
-        serverInfo={serverInfo}
-        addToolCallInfo={(info) => setToolCallInfos([...toolCallInfos, info])}
+        addToolCall={(serverName, info) => setToolCalls([...toolCalls, { serverName, info }])}
       />
     </>
   );
 }
 
 
+// CallToolPanel includes server selection with its own Suspense boundary
 interface CallToolPanelProps {
-  serverInfo: ServerInfo;
-  addToolCallInfo: (toolCallInfo: ToolCallInfo) => void;
+  addToolCall: (serverName: string, info: ToolCallInfo) => void;
 }
-function CallToolPanel({ serverInfo, addToolCallInfo }: CallToolPanelProps) {
+function CallToolPanel({ addToolCall }: CallToolPanelProps) {
+  const [selectedServer, setSelectedServer] = useState(SERVERS[0]);
+  const [serverInfoPromise, setServerInfoPromise] = useState(
+    () => getServerInfo(selectedServer.port)
+  );
+
+  const handleServerChange = (port: number) => {
+    const server = SERVERS.find(s => s.port === port) ?? SERVERS[0];
+    setSelectedServer(server);
+    setServerInfoPromise(getServerInfo(port));
+  };
+
+  return (
+    <div className={styles.callToolPanel}>
+      <label>
+        Server
+        <select
+          value={selectedServer.port}
+          onChange={(e) => handleServerChange(Number(e.target.value))}
+        >
+          {SERVERS.map(({ name, port }) => (
+            <option key={port} value={port}>
+              {name} (:{port})
+            </option>
+          ))}
+        </select>
+      </label>
+      <ErrorBoundary>
+        <Suspense fallback={<p className={styles.connecting}>Connecting to {serverUrl(selectedServer.port)}...</p>}>
+          <ToolCallForm
+            key={selectedServer.port}
+            serverName={selectedServer.name}
+            serverInfoPromise={serverInfoPromise}
+            addToolCall={addToolCall}
+          />
+        </Suspense>
+      </ErrorBoundary>
+    </div>
+  );
+}
+
+
+// ToolCallForm renders inside Suspense - needs serverInfo for tool list
+interface ToolCallFormProps {
+  serverName: string;
+  serverInfoPromise: Promise<ServerInfo>;
+  addToolCall: (serverName: string, info: ToolCallInfo) => void;
+}
+function ToolCallForm({ serverName, serverInfoPromise, addToolCall }: ToolCallFormProps) {
+  const serverInfo = use(serverInfoPromise);
   const toolNames = Array.from(serverInfo.tools.keys());
   const [selectedTool, setSelectedTool] = useState(toolNames[0] ?? "");
   const [inputJson, setInputJson] = useState("{}");
@@ -48,48 +126,47 @@ function CallToolPanel({ serverInfo, addToolCallInfo }: CallToolPanelProps) {
 
   const handleSubmit = () => {
     const toolCallInfo = callTool(serverInfo, selectedTool, JSON.parse(inputJson));
-    addToolCallInfo(toolCallInfo);
+    addToolCall(serverName, toolCallInfo);
   };
 
   return (
-    <div className={styles.callToolPanel}>
-      <form onSubmit={(e) => { e.preventDefault(); handleSubmit(); }}>
-        <label>
-          Tool Name
-          <select
-            value={selectedTool}
-            onChange={(e) => setSelectedTool(e.target.value)}
-          >
-            {toolNames.map((name) => (
-              <option key={name} value={name}>{name}</option>
-            ))}
-          </select>
-        </label>
-        <label>
-          Tool Input
-          <textarea
-            aria-invalid={!isValidJson}
-            value={inputJson}
-            onChange={(e) => setInputJson(e.target.value)}
-          />
-        </label>
-        <button type="submit" disabled={!selectedTool || !isValidJson}>
-          Call Tool
-        </button>
-      </form>
-    </div>
+    <form onSubmit={(e) => { e.preventDefault(); handleSubmit(); }}>
+      <label>
+        Tool
+        <select
+          value={selectedTool}
+          onChange={(e) => setSelectedTool(e.target.value)}
+        >
+          {toolNames.map((name) => (
+            <option key={name} value={name}>{name}</option>
+          ))}
+        </select>
+      </label>
+      <label>
+        Input
+        <textarea
+          aria-invalid={!isValidJson}
+          value={inputJson}
+          onChange={(e) => setInputJson(e.target.value)}
+        />
+      </label>
+      <button type="submit" disabled={!selectedTool || !isValidJson}>
+        Call Tool
+      </button>
+    </form>
   );
 }
 
 
 interface ToolCallInfoPanelProps {
+  serverName: string;
   toolCallInfo: ToolCallInfo;
 }
-function ToolCallInfoPanel({ toolCallInfo }: ToolCallInfoPanelProps) {
+function ToolCallInfoPanel({ serverName, toolCallInfo }: ToolCallInfoPanelProps) {
   return (
     <div className={styles.toolCallInfoPanel}>
       <div className={styles.inputInfoPanel}>
-        <h2 className={styles.toolName}>{toolCallInfo.tool.name}</h2>
+        <h2 className={styles.toolName}>{serverName}:{toolCallInfo.tool.name}</h2>
         <JsonBlock value={toolCallInfo.input} />
       </div>
       <div className={styles.outputInfoPanel}>
@@ -188,8 +265,6 @@ class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
 
 createRoot(document.getElementById("root")!).render(
   <StrictMode>
-    <Suspense fallback={<p>Connecting to server ({MCP_SERVER_URL.href})...</p>}>
-      <Host serverInfoPromise={connectToServer(MCP_SERVER_URL)} />
-    </Suspense>
+    <Host />
   </StrictMode>,
 );
diff --git a/package.json b/package.json
index c73a58c..c15a3c5 100644
--- a/package.json
+++ b/package.json
@@ -30,10 +30,15 @@
     "build:all": "npm run build && npm run examples:build",
     "test": "bun test",
     "examples:build": "find examples -maxdepth 1 -mindepth 1 -type d -exec printf '%s\\0' 'npm run --workspace={} build' ';' | xargs -0 concurrently --kill-others-on-fail",
-    "examples:start": "NODE_ENV=development npm run build && concurrently 'npm run examples:start:basic-host' 'npm run examples:start:basic-server-react'",
+    "examples:start": "NODE_ENV=development npm run build && concurrently 'npm run examples:start:basic-host' 'npm run examples:start:basic-server-react' 'npm run examples:start:basic-server-vanillajs' 'npm run examples:start:budget-allocator-server' 'npm run examples:start:cohort-heatmap-server' 'npm run examples:start:customer-segmentation-server' 'npm run examples:start:scenario-modeler-server' 'npm run examples:start:system-monitor-server'",
     "examples:start:basic-host": "npm run --workspace=examples/basic-host start",
-    "examples:start:basic-server-react": "npm run --workspace=examples/basic-server-react start",
-    "examples:start:basic-server-vanillajs": "npm run --workspace=examples/basic-server-vanillajs start",
+    "examples:start:basic-server-react": "PORT=3101 npm run --workspace=examples/basic-server-react start",
+    "examples:start:basic-server-vanillajs": "PORT=3102 npm run --workspace=examples/basic-server-vanillajs start",
+    "examples:start:budget-allocator-server": "PORT=3103 npm run --workspace=examples/budget-allocator-server start",
+    "examples:start:cohort-heatmap-server": "PORT=3104 npm run --workspace=examples/cohort-heatmap-server start",
+    "examples:start:customer-segmentation-server": "PORT=3105 npm run --workspace=examples/customer-segmentation-server start",
+    "examples:start:scenario-modeler-server": "PORT=3106 npm run --workspace=examples/scenario-modeler-server start",
+    "examples:start:system-monitor-server": "PORT=3107 npm run --workspace=examples/system-monitor-server start",
     "watch": "nodemon --watch src --ext ts,tsx --exec 'bun build.bun.ts'",
     "examples:dev": "NODE_ENV=development concurrently 'npm run watch' 'npm run examples:dev:basic-host' 'npm run examples:dev:basic-server-react'",
     "examples:dev:basic-host": "npm run --workspace=examples/basic-host dev",