Demo background agent (#4409)

Co-authored-by: Bryan Morgan <[email protected]>

1 files changed, 217 insertions, 0 deletions

diff --git a/packages/examples/background_agent/demo-background-agent.ts b/packages/examples/background_agent/demo-background-agent.ts
new file mode 100644
index 00000000..9ac568f4
--- /dev/null
+++ b/packages/examples/background_agent/demo-background-agent.ts
@@ -0,0 +1,217 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
+import { z } from 'zod';
+
+const BackgroundAgentMessageSchema = z.object({
+  role: z.enum(['user', 'agent']),
+  parts: z.array(z.any()),
+});
+
+const BackgroundAgentTaskStatusSchema = z.object({
+  state: z.enum([
+    'submitted',
+    'working',
+    'input-required',
+    'completed',
+    'canceled',
+    'failed',
+  ]),
+  message: BackgroundAgentMessageSchema.optional(),
+});
+
+const BackgroundAgentTaskSchema = z.object({
+  id: z.string(),
+  status: BackgroundAgentTaskStatusSchema,
+  history: z.array(BackgroundAgentMessageSchema).optional(),
+});
+type BackgroundAgentTask = z.infer<typeof BackgroundAgentTaskSchema>;
+
+const server = new McpServer({
+  name: 'demo-background-agent',
+  version: '1.0.0',
+});
+
+const idToTask = new Map<string, BackgroundAgentTask>();
+
+server.registerTool(
+  'startTask',
+  {
+    title: 'Start a new task',
+    description: 'Launches a new task asynchronously.',
+    inputSchema: { prompt: BackgroundAgentMessageSchema },
+    outputSchema: BackgroundAgentTaskSchema.shape,
+  },
+  ({ prompt }) => {
+    const task: BackgroundAgentTask = {
+      id: crypto.randomUUID(),
+      status: {
+        state: 'submitted',
+        message: prompt,
+      },
+      history: [],
+    };
+
+    idToTask.set(task.id, task);
+
+    return {
+      content: [],
+      structuredContent: task,
+    };
+  },
+);
+
+server.registerTool(
+  'getTask',
+  {
+    title: 'Get a task',
+    inputSchema: { id: z.string() },
+    outputSchema: BackgroundAgentTaskSchema.shape,
+  },
+  ({ id }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+
+    return {
+      content: [],
+      structuredContent: task,
+    };
+  },
+);
+
+server.registerTool(
+  'listTasks',
+  {
+    title: 'Lists tasks',
+    outputSchema: {
+      tasks: z.array(BackgroundAgentTaskSchema),
+    },
+  },
+  () => {
+    const out = {
+      tasks: Array.from(idToTask.values()),
+    };
+    return {
+      content: [],
+      structuredContent: out,
+    };
+  },
+);
+
+server.registerTool(
+  'messageTask',
+  {
+    title: 'Send a message to a task',
+    inputSchema: {
+      id: z.string(),
+      message: BackgroundAgentMessageSchema,
+    },
+  },
+  ({ id, message }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+
+    task.history?.push(message);
+    task.status.message = message;
+
+    const statuses = BackgroundAgentTaskStatusSchema.shape.state.options;
+    const randomStatus = statuses[Math.floor(Math.random() * statuses.length)];
+    task.status.state = randomStatus;
+
+    return {
+      content: [],
+    };
+  },
+);
+
+server.registerTool(
+  'deleteTask',
+  {
+    title: 'Delete a task',
+    inputSchema: { id: z.string() },
+  },
+  ({ id }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+    idToTask.delete(id);
+
+    return {
+      content: [
+        {
+          type: 'text',
+          text: 'Task deleted',
+        },
+      ],
+    };
+  },
+);
+
+server.registerTool(
+  'cancelTask',
+  {
+    title: 'Cancels a task',
+    inputSchema: { id: z.string() },
+  },
+  ({ id }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+    task.status.state = 'canceled';
+
+    return {
+      content: [
+        {
+          type: 'text',
+          text: 'Task cancelled',
+        },
+      ],
+    };
+  },
+);
+
+const transport = new StdioServerTransport();
+await server.connect(transport);