The exclusive groups
- Armor protection: Protection / Blast Protection / Fire Protection / Projectile Protection - pick one per piece.
- Melee damage: Sharpness / Smite / Bane of Arthropods (swords and axes).
- Pickaxe & tool yield: Fortune / Silk Touch.
- Bow: Infinity / Mending.
- Trident: Riptide / Loyalty, and Riptide / Channeling (Loyalty + Channeling is fine).
- Crossbow: Multishot / Piercing.
- Boots movement: Depth Strider / Frost Walker.
- Mace: Density / Breach / Smite / Bane of Arthropods (damage enchantments are exclusive).
Why the anvil blocks them
Conflicting enchantments cannot coexist on one item by design. The anvil checks compatibility before charging you: if either item carries an enchantment incompatible with the other's, the merge is rejected. In the calculator, conflicting picks are greyed out automatically - and the 'Allow conflicts' switch exists only for researching historical version quirks.
Historical exceptions (old versions)
A few combos were possible in specific old versions - for example Protection-type mixing between 1.14 and 1.14.3 pre-1, and Mending + Infinity between 1.9 and 1.11.1. These are irrelevant for modern survival but explain screenshots you may have seen online.
Everything else stacks
Non-conflicting enchantments can all live on one item: a helmet can carry Protection IV, Respiration III, Aqua Affinity I, Unbreaking III and Mending together. The calculator shows exactly which enchantments apply to your selected item and plans the cheapest order for all of them.