Merge pull request modelcontextprotocol#388 from jonathanhefner/system-monitor-static-vs-dynamic

jonathanhefner · web-flow · commit 55f0ef019824 · 2026-01-28T12:41:38.000-06:00
Separate static and dynamic data in `system-monitor-server` tools
diff --git a/examples/system-monitor-server/README.md b/examples/system-monitor-server/README.md
@@ -79,18 +79,24 @@ To test local modifications, use this configuration (replace `~/code/ext-apps` w
 
 ### Server (`server.ts`)
 
-Exposes a single `get-system-stats` tool that returns:
+Exposes two tools demonstrating a polling pattern:
 
-- Raw per-core CPU timing data (idle/total counters)
-- Memory usage (used/total/percentage)
-- System info (hostname, platform, uptime)
+1. **`get-system-info`** (Model-visible) — Returns static system configuration:
+   - Hostname, platform, architecture
+   - CPU model and core count
+   - Total memory
 
-The tool is linked to a UI resource via `_meta.ui.resourceUri`.
+2. **`poll-system-stats`** (App-only, `visibility: ["app"]`) — Returns dynamic metrics:
+   - Per-core CPU timing data (idle/total counters)
+   - Memory usage (used/free/percentage)
+   - Uptime
+
+The Model-visible tool is linked to a UI resource via `_meta.ui.resourceUri`.
 
 ### App (`src/mcp-app.ts`)
 
+- Receives static system info via `ontoolresult` when the host sends the `get-system-info` result
+- Polls `poll-system-stats` every 2 seconds for dynamic metrics
 - Uses Chart.js for the stacked area chart visualization
-- Polls the server tool every 2 seconds
 - Computes CPU usage percentages client-side from timing deltas
 - Maintains a 30-point history (1 minute at 2s intervals)
-- Updates all UI elements on each poll
diff --git a/examples/system-monitor-server/server.ts b/examples/system-monitor-server/server.ts
@@ -13,50 +13,78 @@ import os from "node:os";
 import path from "node:path";
 import si from "systeminformation";
 import { z } from "zod";
-// Schemas - types are derived from these using z.infer
-const CpuCoreSchema = z.object({
-  idle: z.number(),
-  total: z.number(),
-});
 
-const CpuStatsSchema = z.object({
-  cores: z.array(CpuCoreSchema),
-  model: z.string(),
-  count: z.number(),
-});
+// Works both from source (server.ts) and compiled (dist/server.js)
+const DIST_DIR = import.meta.filename.endsWith(".ts")
+  ? path.join(import.meta.dirname, "dist")
+  : import.meta.dirname;
 
-const MemoryStatsSchema = z.object({
-  usedBytes: z.number(),
-  totalBytes: z.number(),
-  usedPercent: z.number(),
-  freeBytes: z.number(),
-  usedFormatted: z.string(),
-  totalFormatted: z.string(),
-});
+// =============================================================================
+// Types and schemas
+// =============================================================================
 
 const SystemInfoSchema = z.object({
   hostname: z.string(),
   platform: z.string(),
   arch: z.string(),
-  uptime: z.number(),
-  uptimeFormatted: z.string(),
+  cpu: z.object({
+    model: z.string(),
+    count: z.number(),
+  }),
+  memory: z.object({
+    totalBytes: z.number(),
+  }),
 });
 
-const SystemStatsSchema = z.object({
-  cpu: CpuStatsSchema,
-  memory: MemoryStatsSchema,
-  system: SystemInfoSchema,
-  timestamp: z.string(),
+type SystemInfo = z.infer<typeof SystemInfoSchema>;
+
+const CpuCoreSchema = z.object({
+  idle: z.number(),
+  total: z.number(),
 });
 
-// Types derived from schemas
 type CpuCore = z.infer<typeof CpuCoreSchema>;
-type MemoryStats = z.infer<typeof MemoryStatsSchema>;
-type SystemStats = z.infer<typeof SystemStatsSchema>;
-// Works both from source (server.ts) and compiled (dist/server.js)
-const DIST_DIR = import.meta.filename.endsWith(".ts")
-  ? path.join(import.meta.dirname, "dist")
-  : import.meta.dirname;
+
+const PollStatsSchema = z.object({
+  cpu: z.object({
+    cores: z.array(CpuCoreSchema),
+  }),
+  memory: z.object({
+    usedBytes: z.number(),
+    usedPercent: z.number(),
+    freeBytes: z.number(),
+  }),
+  uptime: z.object({
+    seconds: z.number(),
+  }),
+  timestamp: z.string(),
+});
+
+type PollStats = z.infer<typeof PollStatsSchema>;
+
+// =============================================================================
+// Static system info (called once by Model-facing tool)
+// =============================================================================
+
+function getSystemInfo(): SystemInfo {
+  const cpuInfo = os.cpus()[0];
+  return {
+    hostname: os.hostname(),
+    platform: `${os.platform()} ${os.arch()}`,
+    arch: os.arch(),
+    cpu: {
+      model: cpuInfo?.model ?? "Unknown",
+      count: os.cpus().length,
+    },
+    memory: {
+      totalBytes: os.totalmem(),
+    },
+  };
+}
+
+// =============================================================================
+// Dynamic polling stats (called repeatedly by app-only tool)
+// =============================================================================
 
 // Returns raw CPU timing data per core (client calculates usage from deltas)
 function getCpuSnapshots(): CpuCore[] {
@@ -67,111 +95,73 @@ function getCpuSnapshots(): CpuCore[] {
     return { idle, total };
   });
 }
-
-function formatUptime(seconds: number): string {
-  const days = Math.floor(seconds / 86400);
-  const hours = Math.floor((seconds % 86400) / 3600);
-  const minutes = Math.floor((seconds % 3600) / 60);
-
-  const parts: string[] = [];
-  if (days > 0) parts.push(`${days}d`);
-  if (hours > 0) parts.push(`${hours}h`);
-  if (minutes > 0) parts.push(`${minutes}m`);
-
-  return parts.length > 0 ? parts.join(" ") : "< 1m";
-}
-
-function formatBytes(bytes: number): string {
-  const units = ["B", "KB", "MB", "GB", "TB"];
-  let value = bytes;
-  let unitIndex = 0;
-
-  while (value >= 1024 && unitIndex < units.length - 1) {
-    value /= 1024;
-    unitIndex++;
-  }
-
-  return `${value.toFixed(1)} ${units[unitIndex]}`;
-}
-
-async function getMemoryStats(): Promise<MemoryStats> {
+async function getPollStats(): Promise<PollStats> {
   const mem = await si.mem();
-  return {
-    usedBytes: mem.active,
-    totalBytes: mem.total,
-    usedPercent: Math.round((mem.active / mem.total) * 100),
-    freeBytes: mem.available,
-    usedFormatted: formatBytes(mem.active),
-    totalFormatted: formatBytes(mem.total),
-  };
-}
-
-async function getStats(): Promise<SystemStats> {
-  const cpuSnapshots = getCpuSnapshots();
-  const cpuInfo = os.cpus()[0];
-  const memory = await getMemoryStats();
   const uptimeSeconds = os.uptime();
 
   return {
     cpu: {
-      cores: cpuSnapshots,
-      model: cpuInfo?.model ?? "Unknown",
-      count: os.cpus().length,
+      cores: getCpuSnapshots(),
+    },
+    memory: {
+      usedBytes: mem.active,
+      usedPercent: Math.round((mem.active / mem.total) * 100),
+      freeBytes: mem.available,
     },
-    memory,
-    system: {
-      hostname: os.hostname(),
-      platform: `${os.platform()} ${os.arch()}`,
-      arch: os.arch(),
-      uptime: uptimeSeconds,
-      uptimeFormatted: formatUptime(uptimeSeconds),
+    uptime: {
+      seconds: uptimeSeconds,
     },
     timestamp: new Date().toISOString(),
   };
 }
 
+// =============================================================================
+// MCP server
+// =============================================================================
+
 export function createServer(): McpServer {
   const server = new McpServer({
     name: "System Monitor Server",
     version: "1.0.0",
   });
 
-  // Register the get-system-stats tool and its associated UI resource
   const resourceUri = "ui://system-monitor/mcp-app.html";
 
+  // Model-facing tool: returns static system configuration
   registerAppTool(
     server,
-    "get-system-stats",
+    "get-system-info",
     {
-      title: "Get System Stats",
+      title: "Get System Info",
       description:
-        "Returns current system statistics including per-core CPU usage, memory, and system info.",
+        "Returns system information, including hostname, platform, CPU info, and memory.",
       inputSchema: {},
-      outputSchema: SystemStatsSchema.shape,
+      outputSchema: SystemInfoSchema.shape,
       _meta: { ui: { resourceUri } },
     },
-    async (): Promise<CallToolResult> => {
-      const stats = await getStats();
+    (): CallToolResult => {
+      const info = getSystemInfo();
       return {
-        content: [{ type: "text", text: JSON.stringify(stats) }],
-        structuredContent: stats,
+        content: [{ type: "text", text: JSON.stringify(info) }],
+        structuredContent: info,
       };
     },
   );
 
-  // App-only tool for polling - used by the UI for periodic refresh
+  // App-only tool: returns dynamic metrics for polling
   registerAppTool(
     server,
-    "refresh-stats",
+    "poll-system-stats",
     {
-      title: "Refresh Stats",
-      description: "Refresh system statistics (app-only, for polling)",
+      title: "Poll System Stats",
+      description:
+        "Returns dynamic system metrics for polling: per-core CPU timing, memory usage, and uptime. App-only.",
       inputSchema: {},
-      outputSchema: SystemStatsSchema.shape,
+      outputSchema: PollStatsSchema.shape,
       _meta: { ui: { visibility: ["app"] } },
     },
     async (): Promise<CallToolResult> => {
-      const stats = await getStats();
+      const stats = await getPollStats();
       return {
         content: [{ type: "text", text: JSON.stringify(stats) }],
         structuredContent: stats,
diff --git a/examples/system-monitor-server/src/mcp-app.ts b/examples/system-monitor-server/src/mcp-app.ts
