"Pet will" is sometimes used loosely to describe both informal instructions and formal legal provisions — worth understanding the difference.
Informal instructions
A written letter naming a caregiver and describing your pet's needs — useful and better than nothing, but not legally binding on its own.
Formal legal provisions
A will provision or pet trust, which carries legal weight and can include enforceable funding for the pet's care.
Use both together — informal instructions provide day-to-day detail, while formal documents provide legal enforceability.
This article is general information, not legal advice. Pet trust and estate planning rules vary by state — consult an estate attorney to set up a legally enforceable arrangement.