Claude Code用のCursorスタイルのデザイナーペンです。ヘッド付きChromiumで任意のウェブページをクリック、範囲選択、または描画すると、Claudeが正確なソースファイル、行番号、CSSセレクタ、スクリーンショットを取得し、すぐに編集・検証ができるようになります。
ビジュアルからソースを取得する3つのモード：
モード | 操作 | Claudeが取得するもの |
element | 要素をホバー＋クリック |
|
area | 範囲をドラッグ |
|
draw | 自由な赤ペン描画、Enterで完了 |
|
すべてのスクリーンショットは/tmpにPNGファイルとして保存され、パスとして返されます。そのため、MCPクライアントがbase64のコンテキスト制限に達することはありません。
Reactのソース解決は、_debugSourceファイバープロパティ（@babel/plugin-transform-react-jsx-sourceによって付与）を介してNext.js開発モードで動作します。本番ビルドではこれらが削除されます。以下の本番環境のソースマッピングを参照してください。
Related MCP server: software-design-mermaid-mcp
You: "Make this button rounder"
Claude: [designer_open http://localhost:3000/dashboard]
Claude: [designer_pick mode=element]
You: *click the button*
Claude: → source: Button.tsx:42
Claude: [Edit Button.tsx add rounded-full]
Claude: [designer_screenshot selector=#cta-btn] ← after screenshot for verification前提条件: Node 18+、Claude Code、動作するmacOS/Linux環境（Playwright Chromium）。
git clone https://github.com/YOUR_USER/designer-mcp.git
cd designer-mcp
npm install
npx playwright install chromium # one-time browser downloadMCPをClaude Codeに登録します（ユーザースコープ＝すべてのセッションで利用可能）：
claude mcp add --scope user designer-mcp node "$(pwd)/index.js"Claudeスキルをインストールして、今後のセッションでワークフローを認識できるようにします：
mkdir -p ~/.claude/skills/designer
cp SKILL.md ~/.claude/skills/designer/SKILL.mdClaude Codeを再起動します。セッション内にdesigner_*ツールとdesigner:スキルが表示されるはずです。
Next.js開発サーバーを起動します（ソースマッピングのため）：
cd your-nextjs-app && npm run dev次に、Claude Codeで以下のように入力します：
"Open http://localhost:3000/settings in the designer and let me pick the header."
Claudeがdesigner_open(...)を呼び出し、続いてdesigner_pick({ mode: "element" })を呼び出します。Chromiumが前面に表示され、カーソルが十字線に変わるので、ヘッダーをクリックします。Claudeはsource.fileNameとlineNumberを取得し、直接編集できるようになります。
単一要素 — elementを使用
1つの領域内の関連する複数の要素 — areaを使用（ボックスをドラッグ。中心が範囲内にあるすべての要素を返します）
視覚的な注釈・説明 — drawを使用（赤ペン、Enterで完了、Escでキャンセル）
_debugSourceは開発専用です。本番ビルドでピッカーを使用するには、next.config.jsでソースマップを有効にします：
module.exports = {
productionBrowserSourceMaps: true,
// ...
};現在、ピッカーは本番環境ではsource: nullを返します。将来のバージョンで、デプロイされたソースマップを通じてセレクタを解決する予定です。プルリクエストを歓迎します。
すべてのツールはMCP経由で公開されており、Claude Codeからはmcp__designer-mcp__*として認識されます。
designer_open(url: string)ヘッド付きChromiumインスタンスを起動または再利用してナビゲートします。macOSではbringToFront()とAppleScriptの呼び出しによりウィンドウを前面に表示します。
designer_pick({ mode?: "element" | "area" | "draw" })ピッカーオーバーレイをアクティブにします。ユーザーが操作を完了すると（またはEscでキャンセル、あるいは180秒のタイムアウトで）値を返します。
designer_screenshot({ selector?: string })ページ全体または特定の要素のPNGを取得します。{ path, bytes }を返します。
designer_close()ブラウザを終了し、Playwrightのリソースを解放します。
Playwrightで制御されたChromiumがヘッド付きで起動します（プロセスごとにシングルトン）。
designer_pickが小さなバニラJSオーバーレイ（picker.js）をページに注入します。オーバーレイの動作：
elementモード — mousemove/clickを追跡し、ホバー対象を青枠で囲み、一意に近いCSSセレクタを解決し、Reactファイバーチェーンを辿って_debugSourceを取得し、MCPに返します。
areaモード — ラバーバンド形式の範囲選択。マウスアップ時に、中心点がボックス内にあるすべての要素を収集します（セレクタで重複排除）。
drawモード — ビューポート全体を覆うキャンバスオーバーレイ。ストロークを点の配列としてキャプチャし、Enterで完了します。
サーバーはwindow.__designerResultを200msごとに最大180秒間ポーリングします。
完了後、適切なスクリーンショット（要素 / 範囲の切り抜き / ビューポート全体）が/tmpに保存され、そのパスが返されます。
プルリクエストを歓迎します。特に以下の分野：
本番環境のソースマップ解決
Kestrel/React Nativeピッカー（現在はWebのみ）
elementモードでの複数要素の蓄積（Cmd+クリックで追加）
VS Codeの「エディタで表示」統合
MIT
Close the designer browser and release resources.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It mentions 'release resources', which hints at cleanup behavior, but does not disclose critical details like whether this is destructive (e.g., closes without saving), requires specific permissions, or has side effects. For a tool with no annotations, this leaves significant behavioral gaps.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, efficient sentence that directly states the tool's purpose with no wasted words. It is appropriately sized and front-loaded, making it easy to understand immediately without unnecessary elaboration.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's simplicity (0 parameters, no output schema, no annotations), the description is adequate but incomplete. It covers the basic action but lacks details on behavioral aspects like what happens to unsaved work or error conditions. For a tool that likely interacts with a browser, more context would be helpful despite the low complexity.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The tool has 0 parameters with 100% schema description coverage, so the schema fully documents the lack of inputs. The description does not add parameter details, which is unnecessary here. Baseline is 4 for 0 parameters, as no additional parameter semantics are needed beyond the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the specific action ('Close') and resource ('the designer browser'), distinguishing it from sibling tools like designer_open (open), designer_pick (pick), and designer_screenshot (capture screenshot). It provides a complete verb+resource combination that is unambiguous.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage when the designer browser is open and resources need releasing, but it does not explicitly state when to use this tool versus alternatives or any prerequisites. It lacks explicit guidance on when-not-to-use or named alternatives, leaving usage context somewhat implied rather than clearly defined.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Open a URL in the designer's headed Chromium (launches it if not running). Use this before designer_pick.
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | URL to navigate to |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It discloses key behavioral traits: it opens a URL, launches Chromium if not running, and is intended as a preparatory step. However, it lacks details on error handling, timeouts, or what happens if the URL is invalid, which are important for a tool that interacts with a browser.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise and front-loaded, with two sentences that efficiently convey the action, conditional behavior, and usage context. Every sentence earns its place by providing essential information without redundancy or fluff.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's low complexity (1 parameter, no output schema, no annotations), the description is mostly complete. It covers purpose, usage, and key behavior. However, it could improve by mentioning potential side effects (e.g., browser window focus) or error scenarios, slightly reducing completeness for a tool that launches external processes.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with the schema fully documenting the 'url' parameter. The description does not add any meaning beyond the schema (e.g., URL format examples or constraints), so it meets the baseline of 3 where the schema does the heavy lifting without extra value from the description.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the specific action ('Open a URL') and the target resource ('in the designer's headed Chromium'), including the conditional behavior ('launches it if not running'). It distinguishes from siblings by mentioning designer_pick as a subsequent step, showing awareness of the tool's role in the workflow.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
It explicitly provides when-to-use guidance by stating 'Use this before designer_pick,' establishing a clear sequence in the workflow. This directly addresses when to use this tool versus alternatives (like designer_screenshot or designer_close) by positioning it as a prerequisite step.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Activate the picker in the designer browser. Three modes: element — user clicks one element; returns { selector, tag, classes, text, html, rect, source, screenshot_path } area — user drags a marquee; returns { rect, elements: [{selector, source, rect, ...}], screenshot_path } draw — user ink-annotates with a red pen, Enter to finish; returns { strokes, viewport, screenshot_path (strokes only), viewport_screenshot_path (full view with drawings) } Esc cancels in any mode. screenshot_path / viewport_screenshot_path point to PNGs in /tmp; open with the Read tool.
| Name | Required | Description | Default |
|---|---|---|---|
| mode | No | element (default) = click one, area = drag marquee, draw = freeform pen |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively describes the interactive nature of the tool (user clicks/drags/annotates), cancellation behavior, and output file handling (PNGs in /tmp). However, it doesn't mention potential side effects like browser focus changes or performance considerations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is efficiently structured with bullet-like formatting for the three modes, each clearly explaining the user interaction and return values. Every sentence adds essential information about functionality, cancellation, or output handling with zero wasted text.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a tool with no annotations and no output schema, the description provides comprehensive context about the interactive process, return data structures, and file outputs. The only minor gap is lack of explicit mention about whether this tool requires specific browser state or permissions.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The schema has 100% description coverage with clear enum values and descriptions. The description adds significant value by detailing what each mode returns (specific data structures like selector, rect, strokes, etc.) and operational differences between modes, going well beyond the schema's basic mode definitions.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool's purpose: 'Activate the picker in the designer browser' with three specific modes (element, area, draw). It distinguishes from siblings like designer_close, designer_open, and designer_screenshot by focusing on interactive element/area selection and annotation rather than basic browser operations or screenshot capture.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides explicit guidance on when to use each mode: element for clicking one element, area for dragging a marquee, and draw for freeform pen annotation. It also specifies 'Esc cancels in any mode' and mentions using the Read tool to open resulting PNGs, giving clear operational context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Screenshot the current page or a specific element selector. Returns { path, bytes } — a filesystem path to a PNG in /tmp that you can Read with the Read tool.
| Name | Required | Description | Default |
|---|---|---|---|
| selector | No | Optional CSS selector |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden and effectively discloses key behaviors: it returns a filesystem path to a PNG in /tmp, specifies the output format ({ path, bytes }), and mentions a follow-up action (Read tool). However, it lacks details on potential errors or limitations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is front-loaded with the core purpose, followed by essential details on output and usage, with every sentence earning its place and no wasted words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool's moderate complexity (screenshot functionality with one optional parameter) and no output schema, the description is mostly complete, covering purpose, output, and a follow-up action, though it could include more on error handling or constraints.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The schema description coverage is 100%, so the baseline is 3. The description adds minimal value beyond the schema by implying the selector is optional and used for targeting elements, but does not provide additional syntax or format details.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb ('Screenshot') and resource ('the current page or a specific element selector'), distinguishing it from sibling tools like designer_close, designer_open, and designer_pick by specifying its unique screenshot functionality.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
It provides clear context for usage by specifying 'the current page or a specific element selector' and mentions an alternative action ('Read with the Read tool'), but does not explicitly state when not to use it or compare directly to sibling tools.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
v0.1.0designer_closedesigner_opendesigner_pickdesigner_screenshotScored across 4 tools
Each tool has a clearly distinct purpose with no overlap: open launches the browser, pick activates the picker with specific modes, screenshot captures images, and close terminates the session. The descriptions clearly differentiate their functions, eliminating any ambiguity in tool selection.
All tool names follow a consistent 'designer_' prefix with descriptive action suffixes (open, pick, screenshot, close), using snake_case uniformly. This predictable pattern makes the tool set easy to navigate and understand at a glance.
With 4 tools, this server is well-scoped for its purpose of browser-based design interactions. Each tool earns its place by covering essential operations: launching, picking elements, capturing screenshots, and cleaning up, without being overly sparse or bloated.
The tool set provides complete lifecycle coverage for the designer domain: it supports opening the browser, interactive element selection, screenshot capture, and proper resource closure. There are no obvious gaps, as all core workflows from initiation to termination are addressed effectively.
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