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I understand to attack you need to make attack rolls, but does casting spells require any kind of test before they can be successfully cast or does the player just declare that the spell has been cast assuming they can. The starter rules don't seem to say.

Spells in questions are things like sleep or mage armor.

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The rules don't say that any check is required to make a spell work, which is how we know that spells happen automatically: casting requires no rolls to be successful in general.

However, many spells (like Fear) do require rolls against your spell save DC at the other end, to see if particular targeted creatures are affected by the spell as it successfully goes off. Other spells require attack rolls to see if the spell's successful effect hits a creature.

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    \$\begingroup\$ I'd add that save rolls and to-hit rolls are abstractions, and what they actually represent depends on the individual spell and is open to interpretation. I for one like the idea of a miss with ray of fire potentially torching some random schmuck's house. :V \$\endgroup\$ – Blue Footed Booby Jan 8 '16 at 14:48
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No: you always cast the spell as long as you have an appropriate slot to spend (if the spell is a leveled spell), take the required time, and provide the necessary components.

To what I think is your intent: does casting the spell require any kind of test before I see the effects I intend?

Sometimes: generally "no," but there are two big classes of exceptions.

Most spells (37 of the 53 in the Starter Set Rulebook, by my count) require nothing other than the declared intent and provision of required elements (slot, time, components). The exceptions fall into two categories described in the Starter Set Rulebook:

Many spells specify that a target can make a saving throw to avoid some or all of a spell's effects.... Some spells require the caster to make an attack roll to determine whether the spell effect hits. (Starter Set Rulebook p.23, Saving Throws and Attack Rolls)

So the specific mention of a saving throw or an attack roll in an individual spell's description may add that requirement. Examples include:

Burning Hands (ibid. p.24)

Each creature in a 15-foot cone must make a Dexterity saving throw...

Guiding Bolt (ibid. p.26:)

Make a ranged spell attack against the target.

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It depends upon the caster's class and the spell.

  • In general, if the casting time is "Action", you use your action.
  • If the casting time is "Bonus Action", you use a bonus action to cast it.
  • If the casting time is "reaction", you can use your reaction to cast it if the triggering condition is met. (EG: Shield - you need to be being attacked to cast it.)
  • Any spell cast by a Wild Mage Sorcerer, except a cantrip, may go wild. Such sorcerers must roll 1d20 for 2+ (no modifiers apply) to avoid the spell going wild.

In general, spending the action, bonus action, or reaction means the spell happens. It is at this point that the spell casting slot is considered to be used. It doesn't matter whether or not the spell affects the target; the slot is used when the spell is cast.

After that, however, other considerations apply.

  • Some spells require to-hit rolls. They indicate this fairly clearly in the spell text. EG: Eldritch Bolt
  • Some spells require saving throws. This is usually indicated clearly in the spell text. Most spells have reduced effect if the save is made, but some (especially cantrips) have no effect on a successful save.
  • A few spells have both a to-hit and a saving throw; each has different effects. (EG: Ice Knife)
  • A few spells have specific reactions that negate their effects. (EG: Magic Missile is nullified by the target being put under a shield spell. In such cases, the spell happens, but has no effect.)

Many spells have area effect - you have to work out who is in the area. (I use clear templates on the grid maps I use for combats, which makes it fast and easy.)

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