/asc-screenshot-resize

name: asc-screenshot-resize
description: Resize and validate App Store screenshots with current asc screenshot-size data and macOS sips. Use when preparing or fixing screenshots for App Store Connect submission.

asc screenshot resize

Use this skill to prepare screenshots for App Store Connect. Do not rely on a hard-coded dimension table in this skill; the CLI owns the current size matrix.

Source of truth

Always discover current accepted sizes from `asc` first:

asc screenshots sizes --output table
asc screenshots sizes --all --output table

For local validation before upload:

asc screenshots validate --path "./screenshots/iphone" --device-type "IPHONE_65" --output table
asc screenshots validate --path "./screenshots/ipad" --device-type "IPAD_PRO_3GEN_129" --output table

Common current device-type anchors:

• `IPHONE_65` for the common 6.5-inch iPhone screenshot set.
• `IPAD_PRO_3GEN_129` for the common 12.9/13-inch iPad screenshot set.

Run `asc screenshots sizes --all` when targeting other display types such as 6.9-inch iPhone, Apple TV, Mac, Vision Pro, iMessage, or Watch.

Workflow

1. Sanitize filenames

macOS screenshots can contain hidden Unicode spaces that make tools fail with "not a valid file". Sanitize before batch work:

python3 -c "
import os
for f in os.listdir('.'):
    clean = f.replace('\u202f', ' ')
    if f != clean:
        os.rename(f, clean)
        print(f'Renamed: {clean}')
"

2. Inspect dimensions and metadata

sips -g pixelWidth -g pixelHeight screenshot.png
sips -g hasAlpha -g space screenshot.png

App Store Connect rejects screenshots with alpha transparency. Strip alpha by round-tripping through JPEG:

sips -s format jpeg input.png --out /tmp/asc-screenshot-no-alpha.jpg
sips -s format png /tmp/asc-screenshot-no-alpha.jpg --out output.png
rm /tmp/asc-screenshot-no-alpha.jpg

Batch-strip alpha from PNGs:

for f in *.png; do
  if sips -g hasAlpha "$f" | grep -q "yes"; then
    sips -s format jpeg "$f" --out /tmp/asc-screenshot-no-alpha.jpg
    sips -s format png /tmp/asc-screenshot-no-alpha.jpg --out "$f"
    rm /tmp/asc-screenshot-no-alpha.jpg
    echo "Stripped alpha: $f"
  fi
done

3. Resize only after choosing a target from asc

Pick a width and height from `asc screenshots sizes --all`. `sips -z` takes height first, then width:

# Example: portrait IPHONE_65 1284 x 2778
sips -z 2778 1284 input.png --out output.png

Batch resize to a chosen target:

mkdir -p resized
for f in *.png; do
  sips -z 2778 1284 "$f" --out "resized/$f"
done

4. Validate outputs with asc

sips -g pixelWidth -g pixelHeight -g hasAlpha resized/*.png
asc screenshots validate --path "./resized" --device-type "IPHONE_65" --output table

5. Upload only after validation

asc screenshots upload --version-localization "LOC_ID" --path "./resized" --device-type "IPHONE_65" --dry-run --output table
asc screenshots upload --version-localization "LOC_ID" --path "./resized" --device-type "IPHONE_65"

Guardrails

• Treat `asc screenshots sizes --all` as authoritative; Apple size requirements change.
• Do not stretch screenshots across incompatible aspect ratios unless the user accepts the visual tradeoff.
• Always output to a separate file or directory to preserve originals.
• Screenshots must be PNG or JPEG and must not include alpha transparency.
• Convert Display P3 or other color spaces to sRGB when needed:

sips -m "/System/Library/ColorSync/Profiles/sRGB IEC61966-2.1.icc" input.png --out output.png

• Prefer `asc screenshots validate` over visual inspection before upload.