Add documentation for MCP prompts (#4897)

Co-authored-by: matt korwel <matt.korwel@gmail.com>
Co-authored-by: Bryan Morgan <bryanmorgan@google.com>

docs/tools/mcp-server.md

@@ -570,3 +570,70 @@ The MCP integration tracks several states:
 - **Conflict resolution:** Tool name conflicts between servers are resolved through automatic prefixing
 
 This comprehensive integration makes MCP servers a powerful way to extend the Gemini CLI's capabilities while maintaining security, reliability, and ease of use.
+
+## MCP Prompts as Slash Commands
+
+In addition to tools, MCP servers can expose predefined prompts that can be executed as slash commands within the Gemini CLI. This allows you to create shortcuts for common or complex queries that can be easily invoked by name.
+
+### Defining Prompts on the Server
+
+Here's a small example of a stdio MCP server that defines prompts:
+
+```ts
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
+import { z } from 'zod';
+
+const server = new McpServer({
+  name: 'prompt-server',
+  version: '1.0.0',
+});
+
+server.registerPrompt(
+  'poem-writer',
+  {
+    title: 'Poem Writer',
+    description: 'Write a nice haiku',
+    argsSchema: { title: z.string(), mood: z.string().optional() },
+  },
+  ({ title, mood }) => ({
+    messages: [
+      {
+        role: 'user',
+        content: {
+          type: 'text',
+          text: `Write a haiku${mood ? ` with the mood ${mood}` : ''} called ${title}. Note that a haiku is 5 syllables followed by 7 syllables followed by 5 syllables `,
+        },
+      },
+    ],
+  }),
+);
+
+const transport = new StdioServerTransport();
+await server.connect(transport);
+```
+
+This can be included in `settings.json` under `mcpServers` with:
+
+```json
+"nodeServer": {
+  "command": "node",
+  "args": ["filename.ts"],
+}
+```
+
+### Invoking Prompts
+
+Once a prompt is discovered, you can invoke it using its name as a slash command. The CLI will automatically handle parsing arguments.
+
+```bash
+/poem-writer --title="Gemini CLI" --mood="reverent"
+```
+
+or, using positional arguments:
+
+```bash
+/poem-writer "Gemini CLI" reverent
+```
+
+When you run this command, the Gemini CLI executes the `prompts/get` method on the MCP server with the provided arguments. The server is responsible for substituting the arguments into the prompt template and returning the final prompt text. The CLI then sends this prompt to the model for execution. This provides a convenient way to automate and share common workflows.