An omamori is a small brocade cloth pouch, sewn shut around a paper or wood slip inscribed with a prayer or the issuing shrine's name, and the pouch is deliberately never meant to be opened, opening it is generally understood to undo whatever protection it carries rather than being a harmless way to see what is inside.
Who prepares and sells them
Shrine and temple staff, miko or priests, prepare and bless omamori themselves, and they are sold rather than given away freely, with the proceeds supporting the shrine, distinct types exist for specific purposes, traffic safety, safe childbirth, exam success, each carrying wording matched to that use.
Yearly renewal and how they are retired
An omamori is generally treated as effective for about a year rather than indefinitely, and the custom is to return the old one to a shrine, often though not necessarily the same one that sold it, for ritual burning, many shrines keep a dedicated collection box for exactly this purpose, rather than throwing a worn omamori into household rubbish once its year is up.
Design as a visual cue to purpose
The exterior brocade is often color and pattern coded to its purpose, a traffic safety omamori commonly differs in design from one sold for safe childbirth or exam success, so a buyer can identify the right one at a glance without needing to read the sealed slip inside, which most owners never see at all across the whole life of the object.