diff --git a/packages/scratch-gui/src/lib/ruby-screenshot.js b/packages/scratch-gui/src/lib/ruby-screenshot.js
index 5834d7c089..9203608d4e 100644
--- a/packages/scratch-gui/src/lib/ruby-screenshot.js
+++ b/packages/scratch-gui/src/lib/ruby-screenshot.js
@@ -13,11 +13,93 @@ const buildFilename = function (projectTitle, spriteName) {
     return `${projectTitle}_${spriteName}_ruby.png`;
 };
 
+/**
+ * Measures the maximum rendered text width across all visible lines
+ * in the Monaco editor, relative to the editor DOM node's left edge.
+ * This is more reliable than pixel scanning because Monaco renders
+ * decorative elements (overview ruler, scrollbar, line highlights)
+ * that span the full editor width.
+ * @param {HTMLElement} editorDomNode - the editor's root DOM node
+ * @returns {number} maximum text right edge in CSS pixels, relative to editorDomNode
+ */
+const measureTextWidth = function (editorDomNode) {
+    const viewLines = editorDomNode.querySelector('.view-lines');
+    if (!viewLines) return 0;
+
+    const editorLeft = editorDomNode.getBoundingClientRect().left;
+    let maxRight = 0;
+
+    for (const line of viewLines.children) {
+        const spans = line.querySelectorAll('span span');
+        for (const span of spans) {
+            const right = span.getBoundingClientRect().right;
+            if (right > maxRight) maxRight = right;
+        }
+    }
+
+    return maxRight > 0 ? maxRight - editorLeft : 0;
+};
+
+/**
+ * Measures the maximum rendered furigana annotation width.
+ * ViewZones may extend beyond the code text width.
+ * @param {HTMLElement} editorDomNode - the editor's root DOM node
+ * @returns {number} maximum furigana right edge in CSS pixels, relative to editorDomNode
+ */
+const measureFuriganaWidth = function (editorDomNode) {
+    const viewZones = editorDomNode.querySelector('.view-zones');
+    if (!viewZones) return 0;
+
+    const editorLeft = editorDomNode.getBoundingClientRect().left;
+    let maxRight = 0;
+
+    const spans = viewZones.querySelectorAll('span');
+    for (const span of spans) {
+        const right = span.getBoundingClientRect().right;
+        if (right > maxRight) maxRight = right;
+    }
+
+    return maxRight > 0 ? maxRight - editorLeft : 0;
+};
+
+/**
+ * Crops a PNG blob to the specified width.
+ * Returns the original blob if cropping would not reduce the width.
+ * @param {Blob} blob - source PNG blob
+ * @param {number} cropWidth - target width in image pixels
+ * @returns {Promise<Blob>} cropped (or original) PNG blob
+ */
+const cropToWidth = async function (blob, cropWidth) {
+    const bitmap = await createImageBitmap(blob);
+    const {width, height} = bitmap;
+
+    // No crop needed if target width >= image width
+    if (cropWidth >= width) {
+        bitmap.close();
+        return blob;
+    }
+
+    const canvas = document.createElement('canvas');
+    canvas.width = cropWidth;
+    canvas.height = height;
+    const ctx = canvas.getContext('2d');
+    ctx.drawImage(bitmap, 0, 0, cropWidth, height, 0, 0, cropWidth, height);
+    bitmap.close();
+
+    return new Promise(resolve => {
+        canvas.toBlob(croppedBlob => {
+            resolve(croppedBlob || blob);
+        }, 'image/png');
+    });
+};
+
 /**
  * Captures the Monaco editor content as a PNG image and triggers a download.
  * Temporarily expands the editor to its full content height so that all lines
  * (including those scrolled out of view) are rendered in the DOM before capture.
  * ViewZones (e.g. furigana annotations) are captured naturally as DOM elements.
+ * After capture, the image is cropped to the actual text content width to remove
+ * the large right-side whitespace caused by the editor being wider than the code.
  * @param {object} editor - Monaco editor instance
  * @param {string} projectTitle - Project name (used in filename)
  * @param {string} spriteName - Sprite / stage name (used in filename)
@@ -39,6 +121,10 @@ const downloadRubyAsImage = async function (editor, projectTitle, spriteName) {
     const originalHeight = containerEl.style.height;
     const originalOverflow = containerEl.style.overflow;
 
+    /** Extra pixels (CSS) added to the right of the content boundary. */
+    const CROP_PADDING = 16;
+    const PIXEL_RATIO = 2;
+
     try {
         // Disable scrollBeyondLastLine to get tight content height
         editor.updateOptions({scrollBeyondLastLine: false});
@@ -59,17 +145,29 @@ const downloadRubyAsImage = async function (editor, projectTitle, spriteName) {
             });
         });
 
+        // Measure content width from rendered DOM before capture
+        const textWidth = measureTextWidth(editorDomNode);
+        const furiganaWidth = measureFuriganaWidth(editorDomNode);
+        const contentWidth = Math.max(textWidth, furiganaWidth);
+
         // Capture the editor DOM as a PNG blob.
         // skipFonts avoids SecurityError when html-to-image tries to read
         // cssRules from cross-origin stylesheets (Monaco's CDN CSS).
         const blob = await toBlob(editorDomNode, {
             backgroundColor: '#ffffff',
-            pixelRatio: 2,
+            pixelRatio: PIXEL_RATIO,
             skipFonts: true
         });
 
         if (blob) {
-            downloadBlob(buildFilename(projectTitle, spriteName), blob);
+            let downloadableBlob = blob;
+            if (contentWidth > 0) {
+                const cropWidthPx = Math.ceil(
+                    (contentWidth + CROP_PADDING) * PIXEL_RATIO
+                );
+                downloadableBlob = await cropToWidth(blob, cropWidthPx);
+            }
+            downloadBlob(buildFilename(projectTitle, spriteName), downloadableBlob);
         }
     } finally {
         // Restore original state
@@ -84,5 +182,8 @@ const downloadRubyAsImage = async function (editor, projectTitle, spriteName) {
 
 export {
     buildFilename,
+    cropToWidth,
+    measureFuriganaWidth,
+    measureTextWidth,
     downloadRubyAsImage
 };
diff --git a/packages/scratch-gui/test/unit/lib/ruby-screenshot.test.js b/packages/scratch-gui/test/unit/lib/ruby-screenshot.test.js
index 1afc7d7afa..551231de24 100644
--- a/packages/scratch-gui/test/unit/lib/ruby-screenshot.test.js
+++ b/packages/scratch-gui/test/unit/lib/ruby-screenshot.test.js
@@ -1,5 +1,8 @@
 import {
     buildFilename,
+    cropToWidth,
+    measureTextWidth,
+    measureFuriganaWidth,
     downloadRubyAsImage
 } from '../../../src/lib/ruby-screenshot';
 
@@ -52,11 +55,150 @@ describe('buildFilename', () => {
     });
 });
 
+// ---- measureTextWidth ----
+
+describe('measureTextWidth', () => {
+    test('returns 0 when .view-lines is not found', () => {
+        const div = document.createElement('div');
+        expect(measureTextWidth(div)).toBe(0);
+    });
+
+    test('measures max right edge of text spans', () => {
+        const editor = document.createElement('div');
+        const viewLines = document.createElement('div');
+        viewLines.classList.add('view-lines');
+
+        // Create two lines with spans at different widths
+        const line1 = document.createElement('div');
+        const span1 = document.createElement('span');
+        const innerSpan1 = document.createElement('span');
+        innerSpan1.textContent = 'short';
+        span1.appendChild(innerSpan1);
+        line1.appendChild(span1);
+
+        const line2 = document.createElement('div');
+        const span2 = document.createElement('span');
+        const innerSpan2 = document.createElement('span');
+        innerSpan2.textContent = 'this is a longer line of code';
+        span2.appendChild(innerSpan2);
+        line2.appendChild(span2);
+
+        viewLines.appendChild(line1);
+        viewLines.appendChild(line2);
+        editor.appendChild(viewLines);
+        document.body.appendChild(editor);
+
+        // jsdom returns 0 for getBoundingClientRect, so result is 0
+        // but the function should not throw
+        const width = measureTextWidth(editor);
+        expect(typeof width).toBe('number');
+
+        document.body.removeChild(editor);
+    });
+});
+
+// ---- measureFuriganaWidth ----
+
+describe('measureFuriganaWidth', () => {
+    test('returns 0 when .view-zones is not found', () => {
+        const div = document.createElement('div');
+        expect(measureFuriganaWidth(div)).toBe(0);
+    });
+
+    test('returns 0 when view-zones has no spans', () => {
+        const editor = document.createElement('div');
+        const viewZones = document.createElement('div');
+        viewZones.classList.add('view-zones');
+        editor.appendChild(viewZones);
+        expect(measureFuriganaWidth(editor)).toBe(0);
+    });
+});
+
+// ---- cropToWidth ----
+
+describe('cropToWidth', () => {
+    afterEach(() => {
+        document.createElement.mockRestore?.();
+        delete global.createImageBitmap;
+    });
+
+    test('crops blob to specified width', async () => {
+        const imgWidth = 1000;
+        const imgHeight = 500;
+        global.createImageBitmap = jest.fn(() =>
+            Promise.resolve({width: imgWidth, height: imgHeight, close: jest.fn()})
+        );
+
+        const canvases = [];
+        const mockCtx = {drawImage: jest.fn()};
+        const realCreateElement = document.createElement.bind(document);
+        jest.spyOn(document, 'createElement').mockImplementation(tag => {
+            const el = realCreateElement(tag);
+            if (tag === 'canvas') {
+                canvases.push(el);
+                el.getContext = jest.fn(() => mockCtx);
+                el.toBlob = jest.fn(cb => cb(new Blob(['cropped'], {type: 'image/png'})));
+            }
+            return el;
+        });
+
+        const inputBlob = new Blob(['original'], {type: 'image/png'});
+        const result = await cropToWidth(inputBlob, 400);
+
+        expect(result).not.toBe(inputBlob);
+        expect(canvases[0].width).toBe(400);
+        expect(canvases[0].height).toBe(imgHeight);
+        expect(mockCtx.drawImage).toHaveBeenCalledTimes(1);
+    });
+
+    test('returns original blob when cropWidth >= image width', async () => {
+        global.createImageBitmap = jest.fn(() =>
+            Promise.resolve({width: 200, height: 100, close: jest.fn()})
+        );
+
+        const inputBlob = new Blob(['original'], {type: 'image/png'});
+        const result = await cropToWidth(inputBlob, 300);
+
+        expect(result).toBe(inputBlob);
+    });
+
+    test('returns original blob when cropWidth equals image width', async () => {
+        global.createImageBitmap = jest.fn(() =>
+            Promise.resolve({width: 200, height: 100, close: jest.fn()})
+        );
+
+        const inputBlob = new Blob(['original'], {type: 'image/png'});
+        const result = await cropToWidth(inputBlob, 200);
+
+        expect(result).toBe(inputBlob);
+    });
+});
+
 // ---- downloadRubyAsImage ----
 
 describe('downloadRubyAsImage', () => {
     beforeEach(() => {
         jest.clearAllMocks();
+        // Mock createImageBitmap for cropToWidth called inside downloadRubyAsImage.
+        // Return a small image so cropping can work when contentWidth > 0.
+        global.createImageBitmap = jest.fn(() =>
+            Promise.resolve({width: 2000, height: 400, close: jest.fn()})
+        );
+        const mockCtx = {drawImage: jest.fn()};
+        const realCreateElement = document.createElement.bind(document);
+        jest.spyOn(document, 'createElement').mockImplementation(tag => {
+            const el = realCreateElement(tag);
+            if (tag === 'canvas') {
+                el.getContext = jest.fn(() => mockCtx);
+                el.toBlob = jest.fn(cb => cb(new Blob(['cropped'], {type: 'image/png'})));
+            }
+            return el;
+        });
+    });
+
+    afterEach(() => {
+        document.createElement.mockRestore?.();
+        delete global.createImageBitmap;
     });
 
     test('does nothing when editor is null', async () => {
@@ -108,6 +250,7 @@ describe('downloadRubyAsImage', () => {
 
         await downloadRubyAsImage(editor, 'MyProject', 'Cat');
 
+        // In jsdom, measureTextWidth returns 0, so no crop → original blob
         expect(downloadBlob).toHaveBeenCalledWith('MyProject_Cat_ruby.png', mockBlob);
     });