Jess is a short, warm, immediately friendly name that works on both dogs and cats with equal comfort. It's a nickname that functions as a full name — short for Jessica or Jesse depending on the animal's gender signals — and it has the quality of a name that sounds like the owner knows their pet intimately and doesn't need the formality of a full name.
The Nickname-as-Name Tradition
Jess, Max, Ben, Kate — plenty of pets carry names that feel like they've already been shortened from something longer, even when they haven't been. Jess specifically has warm associations with competent, likable characters: think literary Jessicas, athletic Jessies, easygoing companions. Border Collies and other intelligent working breeds suit Jess particularly well — it's a working dog name as much as a companion name.
Human-Pet Crossover
Jess as a human name operates almost always as a nickname for Jessica or Jesse, which means most people encountering a pet named Jess will automatically imagine a full name behind it. That assumption gives the name a sense of depth even in its brief form. Jessica as a full pet name is also an option for owners who want the ceremony of using the whole name.
The Counter-Reading: Almost Too Plain
Jess is so agreeable and unassuming that it risks blending into the background of pet names. It doesn't invite comment or conversation. For owners who value a name that their pet simply answers to without drama or explanation, that's a feature. For owners who want a name that tells a story, Jess offers very little raw material.