diff --git a/claudetool/browse/README.md b/claudetool/browse/README.md
index 6c03e1a..7cc3437 100644
--- a/claudetool/browse/README.md
+++ b/claudetool/browse/README.md
@@ -14,6 +14,7 @@
 6. `browser_eval` - Evaluate JavaScript in the browser context
 7. `browser_screenshot` - Take a screenshot of the page or a specific element
 8. `browser_scroll_into_view` - Scroll an element into view
+9. `browser_resize` - Resize the browser window to specific dimensions
 
 ## Usage
 
diff --git a/claudetool/browse/browse.go b/claudetool/browse/browse.go
index a5a1621..8a72390 100644
--- a/claudetool/browse/browse.go
+++ b/claudetool/browse/browse.go
@@ -655,6 +655,71 @@
 	return llm.TextContent(successResponse()), nil
 }
 
+// ResizeTool definition
+type resizeInput struct {
+	Width   int    `json:"width"`
+	Height  int    `json:"height"`
+	Timeout string `json:"timeout,omitempty"`
+}
+
+// NewResizeTool creates a tool for resizing the browser window
+func (b *BrowseTools) NewResizeTool() *llm.Tool {
+	return &llm.Tool{
+		Name:        "browser_resize",
+		Description: "Resize the browser window to a specific width and height",
+		InputSchema: json.RawMessage(`{
+			"type": "object",
+			"properties": {
+				"width": {
+					"type": "integer",
+					"description": "Window width in pixels"
+				},
+				"height": {
+					"type": "integer",
+					"description": "Window height in pixels"
+				},
+				"timeout": {
+					"type": "string",
+					"description": "Timeout as a Go duration string (default: 5s)"
+				}
+			},
+			"required": ["width", "height"]
+		}`),
+		Run: b.resizeRun,
+	}
+}
+
+func (b *BrowseTools) resizeRun(ctx context.Context, m json.RawMessage) ([]llm.Content, error) {
+	var input resizeInput
+	if err := json.Unmarshal(m, &input); err != nil {
+		return llm.TextContent(errorResponse(fmt.Errorf("invalid input: %w", err))), nil
+	}
+
+	browserCtx, err := b.GetBrowserContext()
+	if err != nil {
+		return llm.TextContent(errorResponse(err)), nil
+	}
+
+	// Create a timeout context for this operation
+	timeoutCtx, cancel := context.WithTimeout(browserCtx, parseTimeout(input.Timeout))
+	defer cancel()
+
+	// Validate dimensions
+	if input.Width <= 0 || input.Height <= 0 {
+		return llm.TextContent(errorResponse(fmt.Errorf("invalid dimensions: width and height must be positive"))), nil
+	}
+
+	// Resize the browser window
+	err = chromedp.Run(timeoutCtx,
+		chromedp.EmulateViewport(int64(input.Width), int64(input.Height)),
+	)
+	if err != nil {
+		return llm.TextContent(errorResponse(err)), nil
+	}
+
+	return llm.TextContent(successResponse()), nil
+}
+
 // GetTools returns browser tools, optionally filtering out screenshot-related tools
 func (b *BrowseTools) GetTools(includeScreenshotTools bool) []*llm.Tool {
 	tools := []*llm.Tool{
@@ -665,6 +730,7 @@
 		b.NewGetTextTool(),
 		b.NewEvalTool(),
 		b.NewScrollIntoViewTool(),
+		b.NewResizeTool(),
 	}
 
 	// Add screenshot-related tools if supported
diff --git a/claudetool/browse/browse_test.go b/claudetool/browse/browse_test.go
index ae4fefd..7cffa0e 100644
--- a/claudetool/browse/browse_test.go
+++ b/claudetool/browse/browse_test.go
@@ -12,6 +12,7 @@
 	"time"
 
 	"github.com/chromedp/chromedp"
+	"github.com/stretchr/testify/require"
 	"sketch.dev/llm"
 )
 
@@ -72,7 +73,7 @@
 	// Test with screenshot tools included
 	t.Run("with screenshots", func(t *testing.T) {
 		toolsWithScreenshots := tools.GetTools(true)
-		if len(toolsWithScreenshots) != 9 {
+		if len(toolsWithScreenshots) != 10 {
 			t.Errorf("expected 9 tools with screenshots, got %d", len(toolsWithScreenshots))
 		}
 
@@ -87,7 +88,7 @@
 	// Test without screenshot tools
 	t.Run("without screenshots", func(t *testing.T) {
 		noScreenshotTools := tools.GetTools(false)
-		if len(noScreenshotTools) != 7 {
+		if len(noScreenshotTools) != 8 {
 			t.Errorf("expected 7 tools without screenshots, got %d", len(noScreenshotTools))
 		}
 	})
@@ -304,3 +305,42 @@
 		t.Errorf("Expected Data in second content")
 	}
 }
+
+// TestResizeTool tests the browser resize functionality
+func TestResizeTool(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	// Skip if CI or headless testing environment
+	if os.Getenv("CI") != "" || os.Getenv("HEADLESS_TEST") != "" {
+		t.Skip("Skipping browser test in CI/headless environment")
+	}
+
+	t.Run("ResizeWindow", func(t *testing.T) {
+		tools := NewBrowseTools(ctx)
+		defer tools.Close()
+
+		// Resize to mobile dimensions
+		resizeTool := tools.NewResizeTool()
+		input := json.RawMessage(`{"width": 375, "height": 667}`)
+		content, err := resizeTool.Run(ctx, input)
+		require.NoError(t, err)
+		require.Contains(t, content[0].Text, "success")
+
+		// Navigate to a test page and verify using JavaScript to get window dimensions
+		navInput := json.RawMessage(`{"url": "https://example.com"}`)
+		content, err = tools.NewNavigateTool().Run(ctx, navInput)
+		require.NoError(t, err)
+		require.Contains(t, content[0].Text, "success")
+
+		// Check dimensions via JavaScript
+		evalInput := json.RawMessage(`{"expression": "({width: window.innerWidth, height: window.innerHeight})"}`)
+		content, err = tools.NewEvalTool().Run(ctx, evalInput)
+		require.NoError(t, err)
+
+		// The dimensions might not be exactly what we set (browser chrome, etc.)
+		// but they should be close
+		require.Contains(t, content[0].Text, "width")
+		require.Contains(t, content[0].Text, "height")
+	})
+}
diff --git a/claudetool/browse/browser_resize.go b/claudetool/browse/browser_resize.go
new file mode 100644
index 0000000..557ea66
--- /dev/null
+++ b/claudetool/browse/browser_resize.go
@@ -0,0 +1,2 @@
+// Package browse contains browser automation tools
+package browse