diff --git a/docs/07_tools.md b/docs/07_tools.md
index ffb8552c..32b04cc0 100644
--- a/docs/07_tools.md
+++ b/docs/07_tools.md
@@ -181,6 +181,18 @@ A tool’s __call__ method may return:
 - None
 - a list or tuple containing any of the above
 
+**Image size limit:** When a tool returns a `PIL.Image.Image`, it is the tool’s responsibility to ensure the image does not exceed **2000×2000 px** (longest side ≤ 2000 px). The Claude API enforces a 2000×2000 px per-image limit when more than 20 images are sent in a single request, which is common in agentic loops. Use `downscale_image()` from `askui.utils.image_utils` to downscale images that may be too large:
+
+```python
+from PIL import Image
+from askui.utils.image_utils import downscale_image
+
+image: Image.Image = ...  # your image
+image = downscale_image(image, max_dimension=2000)
+```
+
+This preserves the original aspect ratio and only downscales images whose longest side exceeds the limit.
+
 ### Complete Example
 
 Here’s a greeting tool that demonstrates all the key concepts:
diff --git a/src/askui/utils/image_utils.py b/src/askui/utils/image_utils.py
index 19a5f92c..501f1fbb 100644
--- a/src/askui/utils/image_utils.py
+++ b/src/askui/utils/image_utils.py
@@ -227,6 +227,33 @@ def scale_image_to_fit(
     return _center_image_in_background(scaled_image, target_size)
 
 
+def downscale_image(
+    image: Image.Image,
+    max_dimension: int = 2000,
+) -> Image.Image:
+    """Downscale an image so its longest side does not exceed `max_dimension`.
+
+    Preserves the original aspect ratio. Images that are already
+    within the limit are returned unchanged.
+
+    Args:
+        image (Image.Image): The PIL Image to downscale.
+        max_dimension (int, optional): Maximum allowed size for the longest side. Defaults to `2000`.
+
+    Returns:
+        Image.Image: The downscaled image, or the original if no scaling was needed.
+    """
+    longest_side = max(image.width, image.height)
+    if longest_side <= max_dimension:
+        return image
+    scale_factor = max_dimension / longest_side
+    new_size = (
+        int(image.width * scale_factor),
+        int(image.height * scale_factor),
+    )
+    return image.resize(new_size, Image.Resampling.LANCZOS)
+
+
 def _scale_coordinates(
     coordinates: tuple[int, int],
     offset: tuple[int, int],