Generally, a healthy leopard gecko will have a tail at least as thick as its neck, bright eyes, ready to eat, and will be active (at night or near dusk/dawn). Signs of an unhealthy leopard gecko include vomiting (unless your leopard gecko hasn’t eaten in awhile and just ate a lot of crickets), lack of appetite, crusty, dull, or sunken eyes, moving slowly (not wanting to eat and keeping close to the ground), a skinny tail (which indicates that he needs more vitamins and minerals), or could have mites, unshed skin, or infections.
How to Take Care of Leopard Geckos 