Add MCP server-level instructions to both packages

.changeset/mcp-server-instructions.md

@@ -0,0 +1,23 @@
+---
+'@storybook/mcp': minor
+'@storybook/addon-mcp': minor
+---
+
+Add MCP server-level instructions to both packages
+
+Both `@storybook/mcp` and `@storybook/addon-mcp` now include server instructions in the MCP `initialize` response. These instructions guide agents on how to use the available tools effectively without requiring explicit prompting from users.
+
+**`@storybook/mcp` instructions include:**
+
+- Tool workflow: when to use `list-all-documentation` vs `get-documentation` vs `get-documentation-for-story`
+- Anti-hallucination rules: never assume component props or API shape
+- Multi-source behavior guidance
+
+**`@storybook/addon-mcp` instructions compose the `@storybook/mcp` baseline and add:**
+
+- Always call `get-storybook-story-instructions` before writing or editing stories
+- `preview-stories` usage expectations
+- `run-story-tests` workflow expectations
+- Toolset availability guidance (`dev`, `docs`, `test`)
+
+The `@storybook/mcp` package also exports `STORYBOOK_MCP_INSTRUCTIONS` for consumers who want to reuse or extend the base instructions.

packages/addon-mcp/README.md

@@ -134,7 +134,9 @@ For clients not listed above, consult their documentation for MCP server configu
 
 ## Usage
 
-This addon provides MCP tools that your agent can use. The goal is that the agent uses these tools automatically when doing UI development, but agents are unreliable and unpredictable, so sometimes you might need to explicitly tell it to use the tools.
+This addon provides MCP tools that your agent can use. When an MCP client connects, the server sends instructions in the `initialize` response to guide agents on how to use the tools effectively — including when to call `get-storybook-story-instructions` before editing stories, how to use preview URLs, and when documentation tools are available. These instructions help agents use the correct workflow implicitly without needing explicit prompting.
+
+The goal is that the agent uses these tools automatically when doing UI development, but agents are unreliable and unpredictable, so sometimes you might need to explicitly tell it to use the tools.
 
 **If you are prompting from an IDE like VSCode or Cursor, be sure to use `Agent` mode and `sonnet-4.5` or better.**
 

packages/addon-mcp/src/instructions/mcp-server-instructions.md

@@ -0,0 +1,35 @@
+# Storybook Addon MCP Server Instructions
+
+This server provides tools to help you build, preview, and test Storybook UI components.
+
+## Before Writing or Editing Stories
+
+Always call **get-storybook-story-instructions** first to get framework-specific guidance. This tool returns the correct imports, patterns, and conventions for the current project. Do not skip this step.
+
+## Story Preview Workflow
+
+After writing or modifying a component or story, call **preview-stories** to retrieve the live preview URLs. Always include these URLs in your response so the user can verify the visual output.
+
+## Story Testing Workflow
+
+When tests are available (run-story-tests tool is present), run tests after writing or changing stories. Fix any failures before reporting success. Do not report stories as complete if tests are failing.
+
+## Component Documentation Workflow (docs toolset)
+
+When the docs toolset is available:
+
+1. Call **list-all-documentation** once to discover available components and docs IDs.
+2. Call **get-documentation** with a specific ID to retrieve full component props, usage examples, and stories.
+3. Call **get-documentation-for-story** when you need documentation scoped to a specific story variant.
+4. Never assume prop names, variants, or component API — always retrieve documentation first.
+5. Only reference IDs returned by list-all-documentation. Do not guess IDs.
+
+## Toolset Availability
+
+Tools are grouped into toolsets. Check which tools are available before assuming a workflow is possible:
+
+- **dev**: preview-stories, get-storybook-story-instructions
+- **docs**: list-all-documentation, get-documentation, get-documentation-for-story
+- **test**: run-story-tests
+
+Toolsets can be restricted per-request via the `X-MCP-Toolsets` header. When a toolset's tools are not listed, that toolset is disabled for this request.

packages/addon-mcp/src/mcp-handler.test.ts

@@ -278,6 +278,9 @@ describe('mcpServerHandler', () => {
 			},
 		});
 		expect(parsedResponse.result.serverInfo.version).toBeDefined();
+		expect(parsedResponse.result.instructions).toBeDefined();
+		expect(parsedResponse.result.instructions).toContain('get-storybook-story-instructions');
+		expect(parsedResponse.result.instructions).toContain('list-all-documentation');
 	});
 
 	it('should respect disableTelemetry setting', async () => {

packages/addon-mcp/src/mcp-handler.ts

@@ -8,6 +8,7 @@ import {
 	addListAllDocumentationTool,
 	addGetDocumentationTool,
 	addGetStoryDocumentationTool,
+	STORYBOOK_MCP_INSTRUCTIONS,
 	type Source,
 } from '@storybook/mcp';
 import type { Options } from 'storybook/internal/types';
@@ -21,6 +22,9 @@ import { addRunStoryTestsTool } from './tools/run-story-tests.ts';
 import { estimateTokens } from './utils/estimate-tokens.ts';
 import { isAddonA11yEnabled } from './utils/is-addon-a11y-enabled.ts';
 import type { CompositionAuth } from './auth/index.ts';
+import addonInstructions from './instructions/mcp-server-instructions.md';
+
+const MCP_SERVER_INSTRUCTIONS = `${STORYBOOK_MCP_INSTRUCTIONS}\n\n${addonInstructions}`;
 
 let transport: HttpTransport<AddonContext> | undefined;
 let origin: string | undefined;
@@ -41,6 +45,7 @@ const initializeMCPServer = async (options: Options, multiSource?: boolean) => {
 		},
 		{
 			adapter: new ValibotJsonSchemaAdapter(),
+			instructions: MCP_SERVER_INSTRUCTIONS,
 			capabilities: {
 				tools: { listChanged: true },
 				resources: { listChanged: true },

packages/mcp/README.md

@@ -1,3 +1,11 @@
 # `@storybook/mcp`
 
 The hype is real.
+
+## Server Instructions
+
+When an MCP client connects to this server, it receives server-level instructions in the `initialize` response. These instructions guide agents on how to use the available tools effectively:
+
+- **Tool workflow**: When to use `list-all-documentation`, `get-documentation`, and `get-documentation-for-story`
+- **Anti-hallucination rules**: Never assume component props or API shape — always retrieve documentation first
+- **Multi-source behavior**: How to scope requests when multiple Storybook sources are configured

packages/mcp/bin.ts

@@ -22,7 +22,14 @@ import { addGetDocumentationTool } from './src/tools/get-documentation.ts';
 import type { StorybookContext } from './src/types.ts';
 import { parseArgs } from 'node:util';
 import * as fs from 'node:fs/promises';
-import { basename } from 'node:path';
+import { readFileSync } from 'node:fs';
+import { basename, resolve, dirname } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const serverInstructions = readFileSync(
+	resolve(dirname(fileURLToPath(import.meta.url)), './src/instructions.md'),
+	'utf-8',
+);
 
 const adapter = new ValibotJsonSchemaAdapter();
 const server = new McpServer(
@@ -33,6 +40,7 @@ const server = new McpServer(
 	},
 	{
 		adapter,
+		instructions: serverInstructions,
 		capabilities: {
 			tools: { listChanged: true },
 		},

packages/mcp/src/globals.d.ts

@@ -0,0 +1,4 @@
+declare module '*.md' {
+	const content: string;
+	export default content;
+}

packages/mcp/src/index.test.ts

@@ -95,6 +95,17 @@ describe('createStorybookMcpHandler', () => {
 		);
 	});
 
+	it('should include server instructions in initialize response', async () => {
+		const handler = await createStorybookMcpHandler();
+		await setupClient(handler);
+
+		const instructions = client.getInstructions();
+		expect(instructions).toBeDefined();
+		expect(instructions).toContain('list-all-documentation');
+		expect(instructions).toContain('get-documentation');
+		expect(instructions).toContain('Anti-Hallucination');
+	});
+
 	it('should call onSessionInitialize handler when provided', async () => {
 		const onSessionInitialize = vi.fn();
 		const handler = await createStorybookMcpHandler({ onSessionInitialize });

packages/mcp/src/index.ts

@@ -6,6 +6,9 @@ import { addListAllDocumentationTool } from './tools/list-all-documentation.ts';
 import { addGetStoryDocumentationTool } from './tools/get-documentation-for-story.ts';
 import { addGetDocumentationTool } from './tools/get-documentation.ts';
 import type { StorybookContext } from './types.ts';
+import serverInstructions from './instructions.md';
+
+export { serverInstructions as STORYBOOK_MCP_INSTRUCTIONS };
 
 // Export tools for reuse by addon-mcp
 export { addListAllDocumentationTool, LIST_TOOL_NAME } from './tools/list-all-documentation.ts';
@@ -82,6 +85,7 @@ export const createStorybookMcpHandler = async (
 		},
 		{
 			adapter,
+			instructions: serverInstructions,
 			capabilities: {
 				tools: { listChanged: true },
 			},

packages/mcp/src/instructions.md

@@ -0,0 +1,23 @@
+# Storybook MCP Server Instructions
+
+This server provides access to Storybook component and documentation manifests.
+
+## Tool Workflow
+
+Use tools in this order:
+
+1. **list-all-documentation** — Call once at the start of a task to discover available components and docs entries. Use the returned IDs for subsequent calls. Pass `withStoryIds: true` when you also need story IDs (e.g., for use with `preview-stories` or `get-documentation-for-story`) — this adds story sub-entries to the list.
+
+2. **get-documentation** — Call with a specific `id` from the list to retrieve full component documentation including props, usage examples, and stories. Prefer this over re-calling list when you already know the ID.
+
+3. **get-documentation-for-story** — Call with a story ID when you need documentation scoped to a specific story variant rather than the whole component.
+
+## Anti-Hallucination Rules
+
+- Never assume component props, variants, or API shape. Always retrieve documentation before using a component.
+- If a component or prop is not in the documentation, do not invent it. Tell the user the component was not found.
+- Only reference IDs returned by list-all-documentation. Do not guess IDs.
+
+## Multi-Source Behavior
+
+When multiple Storybook sources are configured, list-all-documentation returns entries from all sources. Use the `storybookId` field in get-documentation to scope requests to a specific source when needed.