The best post I have found about this is on the Akratic Wizardry site here.

There is a Whitebox thief somewhere that uses a Saving Throw with modifiers for Thieves' Skills. (My google-fu fails me.) So I thought about using this mechanic for magic, psychics, or some other weilder of mystic forces.

What follows is thinking aloud, so feel free to skip to the end to get to the conclusion.

The trick is to prevent a first level charcter from being overpowered. 1st level Clerics do not have a spell, 1st level M-U gets one spell. With a skill roll, you can say that the 1st level spell caster using a skil roll gets spell slots like everyone else. With that, what happens if the roll fails? Do you lose the slot?

It seems really limiting to say that the spell caster loses the slot on a failure. Assuming no modifications to the roll, a 1st level character has a ST of 15, so that is a 30% chance of success. Adding a +3 to the roll increases the chance of success to 45%. That seems more fair, a 1st level character character has close to a 50-50 chance to lose a spell slot.

As the character progresses, the chance of success caps at 11th level with 95% odds. Not too bad. What about the chances for more difficult spells?

I could say 3 - Spell Level as a standard adjustment for the spellcaster. This would limit the spell caster to having a 50% chance to cast a 9th level spell. If they are capped at 7th level spells like Clerics, it gets better (60%)

So with two tweaks, I can use the standard M-U or Cleric table for spell casting classes that roll for success. The tweaks are:

  1. Roll d20 against ST + 3 - Spell Level for success.
  2. The spell slot is lost only on a successful roll.

That leaves us with a somewhat unreliable spell caster with the same limits on number of successful spells cast. He or she may get more attempts to cast spells, but absolutely no extra spells.

Doesn't seem fair to have the same advancement tables, yet be a diminished spell caster. While I could change advancement, it makes more sense to me to add a minor ability.

If I learned a form of spell casting that is somewhat unreliable, I would want to find a way to up my chances of successfully casting a spell.

Let's say that this spell caster can create a type of temporary spell focus. This spell focus would allow them to cast one spell successfully without a skill roll. Using a tried and true OSR rule, the cost of the focus would be 100gp per spell level. It will take the spell level number of days to create the focus.

For regular spell casters, this usually applies to creating scrolls to allow for extra spells. For these spell casters that use a skill roll, it would only provide guaranteed spells using up the slots they have available. In other words, a 1st level spell caster could create a focus to guarantee they could successfully cast a 1st level spell. This would count against their spell slots as it is not a scroll.


With three tweaks, you can have a skill based spell caster, with the same tables as Clerics or Magic-Users.

  1. Roll d20 against ST + 3 - Spell Level for success.
  2. The spell slot is lost only on a successful roll.
  3. The spell caster can create items that guarantee spell success, but use the spell slots. The cost of this item is 100gp per level of the spell.

Next post, I hope to look at other alternatives for spell casting.