Start with the space, not the brochure. A dishwasher sits in a bay under the counter, and the bay decides which models are even on the table. Measure before you open a feature list.
Measure the opening
Take the width of the bay at the front, the height from the floor to the underside of the counter, and the depth from the front edge to the back wall. Note where the bay narrows. A corner, a cabinet frame, or a toe kick can take space that a simple width check misses. Write each figure on the same sheet you will carry to the store or open on the listing page.
Check the door and the clearance
A dishwasher door drops forward and needs open floor in front of it. Look at what sits beside the bay, such as a refrigerator, a wall, or a doorway, and whether it limits how far the door can open. Mark that clearance on your sheet. A unit that slides into the bay but cannot open fully is a poor fit for the kitchen you actually use.
Check the hookups
Find where the water supply and the drain come into the bay. Those points are usually fixed. Compare them to what each candidate's installation guide asks for. Ask whether the unit needs a power outlet inside the bay, and whether your existing outlet and cabinet layout can take it. Read the installation guide for the model itself, not only the summary on the box.
Compare the rest last
Racks, cycle choices, noise ratings, and warranty terms matter, but they cannot rescue a unit that will not fit. Keep only the models that pass the bay, door, and hookup checks, then compare those on the features you will use every day. Ask the seller or retailer to state the warranty terms in writing, and read what they cover before you rely on them.
Plan against the age you are replacing
If you are replacing a dishwasher, write down its install year. Age is a planning input, and it tells you when the next replacement may come due. The Dishwasher: typical service life and when to plan page turns an install year into a planning window.