Pat the 4 bone-in, skin-on chicken thighs dry with paper towels.

In a small bowl, combine 4 tablespoons unsalted butter (softened) and 2 teaspoons ranch seasoning until smooth.

Gently loosen the skin on each thigh by sliding your fingers under the skin near the cavity, taking care not to tear it.

Divide the butter mixture: place about 2 teaspoons of the mixture under the skin of each thigh and spread it evenly over the meat under the skin. Use the remaining butter mixture to spread over the top of each thigh.

Preheat the air fryer to 400°F (if your model requires preheating).

Lightly grease the air fryer basket if your model recommends it, then arrange the thighs in a single layer skin side up without overlapping.

Air fry at 400°F for 14–16 minutes, or until the skin is golden brown and an instant-read thermometer inserted into the thickest part of a thigh (avoiding bone) registers 165°F.

Remove the thighs from the air fryer and let rest a few minutes before serving.