This item looks much like a scroll case. However, it has several (3 to 6) bands near the center. These can be rotated around the cylinder, and are typically covered with runes or numbers, though some may have magical writing only visible with certain spells. The premise of a codex is to safely store documents or plans of extreme secrecy or importance. Inside, the paper to be protected is wrapped around a vial of acid or other corrosive substance. When the codex is locked, any attempt to forcibly open it will cause a small hammer to break the vial, destroying the document. Due to their nature, codices are very rare and expensive. However, when a normal lock will not suffice and magic is not an option, they are a viable alternative. Without the proper code, the codex cannot be unlocked.

When unlocked, one end of the codex slides off to reveal the hollow area. However, if this area is pulled with the wrong combination word (ie - someone is trying to guess the password), there is a 10% chance the hammer will break the vial inside.

Because of the nature of a codex, the knock spell is not sufficient to open the container. Since codices consist of at least three separate locking mechanisms, each casting of the knock spell is only able to unlock up to two at a time, meaning that at all times, at least one of the mechanisms remains locked and protecting the information stored inside.