diff --git a/src/resources/extensions/browser-tools/capture.ts b/src/resources/extensions/browser-tools/capture.ts
index 895ffc13b..24dd890df 100644
--- a/src/resources/extensions/browser-tools/capture.ts
+++ b/src/resources/extensions/browser-tools/capture.ts
@@ -10,9 +10,11 @@ import sharp from "sharp";
 import type { CompactPageState, CompactSelectorState } from "./state.js";
 import { formatCompactStateSummary } from "./utils.js";
 
-// Anthropic API rejects images > 2000px in multi-image requests.
-// Cap at 1568px (recommended optimal size) to stay well within limits.
-const MAX_SCREENSHOT_DIM = 1568;
+// Anthropic vision: 1568px is the recommended optimal width. Height is capped
+// generously at 8000px so tall full-page screenshots remain readable rather
+// than being squished into a square constraint.
+const MAX_SCREENSHOT_WIDTH = 1568;
+const MAX_SCREENSHOT_HEIGHT = 8000;
 
 // ---------------------------------------------------------------------------
 // Compact page state capture
@@ -120,9 +122,10 @@ export async function postActionSummary(p: Page, target?: Page | Frame): Promise
 // ---------------------------------------------------------------------------
 
 /**
- * If either dimension of the image buffer exceeds MAX_SCREENSHOT_DIM,
- * downscale proportionally using sharp. Returns the original buffer
- * unchanged if already within limits.
+ * Constrain screenshot dimensions for the Anthropic vision API.
+ * Width is capped at 1568px (optimal) and height at 8000px, each
+ * independently, using `fit: "inside"` so aspect ratio is preserved.
+ * Small images are never upscaled.
  *
  * `page` parameter is retained for ToolDeps signature stability (D008)
  * but is no longer used — all processing is server-side via sharp.
@@ -133,18 +136,17 @@ export async function constrainScreenshot(
 	mimeType: string,
 	quality: number,
 ): Promise<Buffer> {
-	const { width, height } = await sharp(buffer).metadata();
+	const meta = await sharp(buffer).metadata();
+	const width = meta.width;
+	const height = meta.height;
 
-	if (
-		width !== undefined &&
-		height !== undefined &&
-		width <= MAX_SCREENSHOT_DIM &&
-		height <= MAX_SCREENSHOT_DIM
-	) {
-		return buffer;
-	}
+	if (width === undefined || height === undefined) return buffer;
+	if (width <= MAX_SCREENSHOT_WIDTH && height <= MAX_SCREENSHOT_HEIGHT) return buffer;
 
-	const resizer = sharp(buffer).resize(MAX_SCREENSHOT_DIM, MAX_SCREENSHOT_DIM, { fit: "inside" });
+	const resizer = sharp(buffer).resize(MAX_SCREENSHOT_WIDTH, MAX_SCREENSHOT_HEIGHT, {
+		fit: "inside",
+		withoutEnlargement: true,
+	});
 
 	if (mimeType === "image/png") {
 		return Buffer.from(await resizer.png().toBuffer());