Decide your use: cold snack/sandwich (flavor + slice quality) vs baking (melt + browning).
Pick the closest flavor family first (Swiss-style or Gruyère), then match melt behavior (Havarti/Provolone/Mozzarella).
Use a 1:1 swap by weight; if the substitute is stronger (Gruyère), start at ¾:1 and top up with a milder cheese.
For oven baking, shred or slice thin so the cheese melts evenly and doesn’t pool.
Taste the finished dish once melted; adjust seasoning (pepper/ground mustard) if the swap tastes flatter than jarlsberg.