DnD 5e - Casting a Spell
When casting any spell, the same general rules are always followed, regardless of the source of the spellcasting ability.
Each spell has a description detailed which includes some important information about the spell. Each description begins with a block which includes the spell's name, level, school of magic, casting time, range, components, and duration. After this block, the spell's effects and mechanics are described in plain terms.
Most spells require a single Action to cast, but some spells require a Bonus Action, a Reaction, or much more time to cast.
A spell cast with a bonus action is especially swift. You must use a bonus action on your turn to cast the spell, provided that you haven't already taken a bonus action this turn.
If you cast a spell with a Bonus Action casting time, you can't cast another spell during the same turn, except for a cantrip with a casting time of 1 action. This limitation does not extend to spells with a different casting time. If you cast a non-cantrip spell with a casting time other than a Bonus Action, you may not then cast a spell with a Bonus Action casting time.
For example: An Eldritch Knight has a powerful Fighter class feature called Action Surge which lets them take an extra Action on their turn. If an Eldritch Knight were to cast a spell with a Bonus Action casting time then use Action Surge, they would get two Actions on their turn but if they chose to cast more spells they would only be able to cast cantrips. If the Eldritch Knight used Action Surge to cast Fireball twice, that is perfectly fine.
Some spells can be cast as Reactions. These spells take a fraction of a second to bring about and are cast in response to some event. If a spell can be cast as a Reaction, the spell description tells you exactly when you can do so.
For example: the spell feather fall's casting time reads "1 reaction, which you take when you or a creature within 60 feet of you falls". This allows you to cast the spell in time to prevent a creature from taking damage from falling.
Longer Casting Times
Certain spells require more time to cast: minutes or even hours. When you cast a spell with a casting time longer than a single Action or Reaction, you must spend your Action each turn casting the spell, and you must maintain your Concentration while you do so (see "Concentration" below). If your Concentration is broken, the spell fails, but you don't expend a spell slot. If you want to try casting the spell again, you must start over.
Spells cast as Rituals add 10 minutes to their original casting time.
The target of a spell must be within the spell's range. For a spell like magic missile, the target is a creature. For a spell like fireball, the target is the point in space where the ball of fire erupts.
Most spells have ranges expressed in feet. Some spells can target only a creature (including you) that you touch. Other spells, such as the shield spell, affect only you. These spells have a range of "self".
Spells that create cones or lines of effect that originate from you also have a range of "self", indicating that the origin point af the spell's effect must be you (see "Areas af Effect" later in the this chapter).
Once a spell is cast, its effects aren't limited by its range, unless the spell's description says otherwise. For example: the spell flaming sphere creates a ball of flame which the caster can move about for the duration of the spell. Flaming sphere has a range of 60 ft., but after the spell is cast the caster is free to roll the sphere as far away as the like while the spell remains in effect.
Aspell's components are the physical requirements you must meet in order to cast it. Each spell's description indicates whether it requires verbal (V), somatic (S), or material (M) components. If you can't provide all of a spell's components, you are unable to cast the spell.
Casting some spells requires particular objects, specified in parentheses in the component entry. A character can use a component pouch or a spellcasting focus (found on page 151 of the Player's Handbook) in place of the components specified for a spell. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.
If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell.
A spellcaster must have a hand free to access these components or must be holding a spellcasting focus, but it can be the same hand that he or she uses to perform somatic components. If a spell does not require a material component which your spellcasting focus can replace, you can't perform somatic components with the hand which is holding your spellcasting focus.
Spellcasting gestures might include a forceful gesticulation or an intricate set of gestures. If a spell requires a somatic component, the caster must have free use of at least one hand to perform these gestures.
Some creatures have the ability to cast spells but have no hands. The published rules don't specify how this works, but I imagine that they use whatever limbs they do have in place of hands to perform somatic components adapted to their body.
Most spells require the chanting of mystic words. The words themselves aren't the source of the spell's power; rather, the particular combination of sounds, with specific pitch and resonance, sets the threads of magic in motion. Thus, a character who is gagged or in an area of silence, such as one created by the silence spell, can't cast a spell with a verbal component.
Aspell's duration is the length of time the spell persists. Aduration can be expressed in rounds, minutes, hours, or even years. Some spells specify that their effects last until the spells are dispelled or destroyed.
Many spells are instantaneous. The spell harms, heals, creates, or alters a creature or an object in a way that can't be dispelled, beca use its magic exists only for an instant.
Some spells require you to maintain Concentration in order to keep their magic active. If you lose Concentration, such a spell ends. If a spell must be maintained with Concentration, that fact appears in its Duration entry, and the spell specifics how long you can concentrate on it. You can end Concentration at any time (no action required), including on other creatures' turns.
Normal activity, such as moving and attacking, doesn't interfere with concentration. The following factors can break concentration:
Casting Another Spell That Requires Concentration
Vou lose Concentration on a spell if you cast another spell that requires concentration. You can't concentrate on two spells at once.
You're free to cast other spells without issue, even if those spells have a duration longer than Instantaneous, without losing Concentration.
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 Incapacilated or Killed
You lose Concentration on a spell if you are incapacitated or if you die.
The DM might also decide that certain environmental phenomena, such as a wave crashing over you while you're on a storm-tossed ship, require you to succeed on a DC 10 Constitution saving throw to maintain Concentration on a spell.
A typical spell requires you to pick one or more targets to be affected by the spell's magic. A spell's description tells you whether the spell targets creatures, objects, or a point of origin for an area of effect (described below).
Unless a spell has a perceptible effect, a creature might not know it was targeted by a spell at all. An effect like crackling lightning is obvious, but a more subtle effect, such as an attempt to read a creature's thoughts, typically goes unnoticed, unless a spell says otherwise.
If you attempt to target a creature that can't be targeted by the spell, such as using charm person on a beast, the spell fails as though the target had passed the saving throw to negate the effects of the spell. The Dungeon Master is not required to inform you why the spell failed, only that it did so. The creature is only aware that it was targeted by the spell if it would normally notice that it had been targeted (see previous paragraph).
To target something, you must have a clear path to it, so it can't be behind total cover like a solid wall. This is sometimes informally referred to as "line of sight", though "line of sight" isn't a term used by the rules.
If you place an area of effect at a point that you can't see and an obstruction (such as a solid wall) is between you and that point, the point of origin comes into being on the near side of that obstruction. Lesser forms of cover, including creatures, don't block your clear path to a target.
For example: A 1st-level bard wants to cast sleep on a group of goblins who are standing in an adjacent room. The room has a door, but the door is closed, providing total cover to the goblins. The bard casts the spell anyway, so rather than the spell's effect being centered in the middle of the room as intended, the spell's origin point is on the near side on the wall or door, depending on where the bard was standing. The bard, being all by theirself, is the only creature in the area of effect, so they then suffer the full effects of their own spell, potentially putting themself to sleep while the goblins on the other side of the door are totally unaware unless they heard the sounds of the bard casting a spell.
If a spell targets a creature of your choice, you can choose yourself, unless the creature must be hostile or specifically a creature other than you. If you are in the area of effect of a spell you cast, you can target yourself.
Many spells (and other special abilities) use terms like "allies", "an ally", "companions", or "a friendly creature". These terms explicitly do not include you, so you can't target yourself unless unless the effect specifically says so. Usually this will involve language that specifically use the word "you", as in "you or an ally".
Areas of Effect
Spells such as burning hands and cone of cold cover an area, allowing them to affect multiple creatures at once. This area is called an "Area of Effect", commonly abbreviated to "AOE".
A spell's description specities its area af effect, which typically has one of five different shapes: cone, cube, cylinder, line, ar sphere. Every area of effect has a point of origin, a location from which the spell's energy erupts. The roles for each shape specify how you position its point of origin. Typically, a point of origin is a point in space, but some spells have an area whose origin is a creature or an object.
A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover, as explained in chapter 9.
A cone extends in a direction you choose fram its point of origin. A cone's width at a given point along its length is equal to that point's distance from the point of origin, so a cone's maximum width is equal to its length. A cone's area of effect specities its maximum length.
A cone's point of origin is not included in the cone's area of effect, unless you decide otherwise. Because most cone spells have a range of "Self", this means that your space is the point of origin, so if you choose for the cone to affect its point of origin, you are intentionally allowing yourself to be inside the area of effect.
You select a cube's point of origin, which lies anywhere on a face of the cubic effect. The cube's size is expressed as the length of each side.
A cube's point of origin is not included in the cube's area of effect, unless you decide otherwise.
A cylinder's point of origin is the center of a circle of a particular radius, as given in the spell description.
The circle must either be on the ground or at the height of the spell effect, so you cannot place a cylinder on walls, on ceilings, or in mid-air.
The energy in a cylinder expands in straight lines from the point of origin to the perimeter of the circle, forming the base of the cylinder. The spell's effect then shoots up from the base or down from the top, to a distance equal to the height of the cylinder.
A cylinder's point of origin is included in the cylinder's area of effect.
A line extends from its point of origin in a straight path up to its length and covers an area defined by its width.
A line's point of origin is not included in the line's area of effect, unless you decide otherwise. Keep in mind that for many spells, such as lightning bolt, you are the point of origin for the spell, so choosing to target the point of origin may mean targeting yourself.
You select a sphere's point of origin, and the sphere extends outward from that point. The sphere's size is expressed as a radius in feet that extends from the point.
A sphere's point of origin is included in the sphere's area of effect.
Areas of Effect on a Grid
If you're playing on a grid, you're accustomed to your character's position "snapping" into a 5x5 square.
Many spells specify that a target can make a saving throw to avoid some or all of a spell's effects. The spell specifies the ability that the target uses for the save and what happens on a success or failure.
The DC to resist one of your spells equals 8 + your spellcasting ability modifier + your Proficiency Bonus + any special modifiers.
Some spells require the caster to make an attack roll to determine whether the spell effect hits the intended target. Your attack bonus with a spell attack equals your spellcasting ability modifier + your Proficiency Bonus.
Most spells that require attack rolls involve ranged attacks. Remember that you have disadvantage on a ranged attack roll if you are within 5 feet of a hostile creature that can see you and that isn't incapacitated (see chapter 9).
Combining Magical Effects
The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect (such as the highest bonus) from those castings applies while their durations overlap.
For example, if two clerics cast bless on the same target, that character gains the spell's benefit only once; they don't get to roll two bonus dice. Similarly, if those clerics both cast bane on the same target, the effects apply only once. If those clerics instead choose to cast two different spells on the same target, the effects of both spells would apply.