Thẻ Sách Mềm is a free book verification app developed by saokhuee.com for Android users. It helps users to verify the authenticity of textbooks and reference books published by the Vietnam Education Publishing House. The app works by scanning the secret code printed on the Thẻ Sách Mềm, which is attached to the back cover of the book. It then cross-references this code with the sachmem.vn database to confirm the book's authenticity.

With the proliferation of fake and pirated books in the market, Thẻ Sách Mềm is a useful tool for buyers to check the validity of the book's serial number before making a purchase. However, it is important to note that the app only serves as a warning system and does not provide a definitive answer as to whether the book is genuine or not, as the Thẻ Sách Mềm can also be counterfeited with a fake serial number and secret code.