Are the spark plugs labeled for which cylinder they are for?

Spark plugs themselves are usually not labeled for which cylinder they go into. While some high-end or specialized plugs might have markings, it's not a standard practice. The information on which plug goes where is found in your vehicle's repair manual or online resources specific to your vehicle's make, model, and year. Firing order is crucial, and getting them in the wrong cylinder can cause misfires and engine damage.