Preheat oven to 425°F. Line a large rimmed baking sheet with parchment.
Cut potatoes into 1-inch pieces, then pat very dry with towels.
Whisk oil, ranch seasoning, garlic powder, onion powder, paprika, salt, and pepper in a big bowl.
Toss in potatoes until every piece is well coated.
Spread potatoes on the sheet in a single layer, cut sides down if possible.
Roast 20 minutes. Stir, then roast 12–15 minutes more until browned and tender.
Finish with parsley. Taste and adjust salt if needed. Serve hot.