I'm new to D&D and most of the stuff is easily understood (though might require some time spent reading the rules). What has me flummoxed is how casting of bless works for my cleric. I can't figure out how I determine if the cast was successful. I understand the mechanics for attack spells and spells requiring saving throws. But can anyone shed some light on how I determine if the cast for Bless was successful?
In general, if a spell targets allies, it just succeeds if they're willing.
In the case where some mechanical element would be interfering with the spell (anti-magic or counterspell), I don't think there's an explicit mechanical way to be notified if a spell succeeds or fails.
There are no saving throws against Bless. Given that it's an entirely beneficial effect, I don't know why you would.
Unless your concentration is disrupted (someone attacked you while casting), or something directly prevented you from casting the spell (like a no-magic zone), the spell succeeds. "Success" is the default state for "good stuff happens" spells, you'll only need knowledge of if it fails.
Assuming you fulfill all requirements of the spell, it just happens.
Pick up to three creatures within 30 feet of you, spend an action if in combat, and poof, they are #blessed.
Unless there is a specific effect that prevents your spell (counterspell/anti-magic field/etc.) it takes hold.
Spells Do What They Say.
Jeremy Crawford has said numerous times, "Spells do exactly what they say." That if they require a roll, the spell will say so.
Design and History
Older versions of DnD had spell failure. 5e removed it because you're already spending an extremely limited resource (spell slots) to cast it. There are ways to force spells to fail, but there isn't just a random chance the spell does nothing.
When There are Rolls
When casting a battle spell there is typically an attack roll or saving throw to give the opponent an attempt to avoid or decrease the impact of the spell (there are some exceptions like Magic Missle). Missing or the opponent dodging or saving vs damage isn't spell failure; though if there is a single target the effect is basically the same as if there were.
When casting healing or buff spells, the spell typically just works in 5e. The rolls involved (if any) typically tell you how much health/how effective the effect.
So, When is Bless is Successful?
Bless just works when you have a focus or material components, speak the incantation and do the hand motions with a free hand. It is always successful. Once cast it will continue in operation until
- 1 minute passes,
- you cast another concentration spell,
- you use the Ready Action to ready a spell,
- you use a feat or feature that requires you to concentrate as if casting a concentration spell, or
- you take damage and fail the Constitution Save to maintain concentration.
Yes, it is a powerful spell, but it using two resources: concentration and a spell slot.
Largely the actual casting is not the difficult part, If cast during combat, you will spend your action, or outside of combat you can just cast it (but note the 1 minute maximum duration). Keeping the benefits alive can be more difficult.The actual cast is usually not the difficult part.
More detail about concentration:
Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can’t concentrate on two spells at once.
Taking damage. Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration. The DC equals 10 or half the damage you take, whichever number is higher. If you take damage from multiple sources, such as an arrow and a dragon’s breath, you make a separate saving throw for each source of damage.
- Being Incapacitated or killed. You lose concentration on a spell if you are Incapacitated or if you die.
Other than that, be wary of the Mage Slayer feat.
Mage Slayer: You have practiced techniques useful in melee combat against spell casters, gaining the following benefits:
- When a creature within 5 feet of you casts a spell, you can use your reaction to make a melee weapon attack against that creature.
- When you damage a creature that is concentrating on a spell, that creature has disadvantage on the saving throw it makes to maintain its concentration.
- You have advantage on saving throws against spells cast by creatures within 5 feet of you.