Fake SD cards report a larger size than they really have – for example a "512 GB" card that only stores 32 GB. Files written past the real size are lost without warning. APPtoSD PRO can test this before you trust a card with your photos.

Run the full capacity check

Back up anything important on the card first.
Open APPtoSD PRO → SD card tools → Full capacity check.
Start the test and keep the app open. It writes test data to the free space and reads it back.

If the data that is read back does not match, the card is fake or failing. Stop using it for important files and ask the seller for a refund.

Run the speed test

The speed test shows read and write speed with a live graph. A slow card makes moved apps start slowly and videos stutter. For apps and 4K video, choose a card marked A1/A2 or U3/V30.

Note: A full capacity check writes to all free space, so it takes time on large cards. Your existing files are not erased.

When the card is not detected

If the card is missing, ejected, read-only or unreadable, APPtoSD PRO shows what Android reports and the next step to try.