D&D Next (as of the last playtest packet) changed spellcasting from previous versions of the D&D. Spellcasting works basically the same for all spellcasting classes with a few exceptions which I will make note of. Cantrips work a little differently than normal spells, I will explain them after normal spells. First lets start with some definitions.
A Long Rest is resting for an eight hour period with no more than two hours of light activity such as reading, talking, eating, or standing watch and no more than one hour of those spent performing strenuous activities such as combat or travel. If these conditions are exceeded the Long Rest must start over.
A characters Spell List includes all the spells it is possible for that character to cast. Cleric’s, Druid’s, Paladin’s and Ranger’s spell list includes all the spells from their respective class spells that are of a level that they can cast (see below). Mages must choose a number of spells from the Mage spell list to add into their Spellbook. This is now their personal Spell List and these are the only spells they can prepare. Bards are also different, they select a number of spells from the Bard spell list and these become Known Spells which are the only spells they can cast. Mages and Bards add more spells as they increase in level to their Spellbook and Known Spells respectively.
Each caster can prepare a number of spells based on their level (see below). These spells can be of any level the character can cast. These are the only spells the caster will have access to till they prepare spells again (after another long rest) so it is a generally a good idea to prepare at least one spell of each spell level you can cast(see below). You can choose not to prepare some of your spells and prepare them at another time (later in the day for example). Preparing a spell takes one minute of concentration per spell level of each spell prepared. Preparing a 1st and 2nd level spell will take three minutes.
Clerics, Druids and Mages – After a long rest these casters can prepare a number of spells from their Spell List equal to their spell caster level + 1. A 3rd level caster can prepare 4 spells, 4th level caster can prepare 5, etc.
Paladin, Ranger – After a long rest these casters can prepare a number of spells from their Spell List equal to Half their Paladin or Ranger level + 1. A 3rd level Ranger can prepare 2 spells, a 4th level Paladin can prepare 3, etc.
Bard – Bards do not need to prepare spells.
Daily Spells or Spell slots:
After a long rest a character can cast a number of spells of each spell level available to them based on their caster level. See each class for details on the number of spells they can each cast per day. These spells can only be Prepared Spells which is why it is useful to prepare at least one spell from each spell level you can cast. After you have cast your limit of spells you must take a long rest before you can cast again.
Bards are an exception, they only cast from their list of Known Spells as they do not Prepare spells but they otherwise follow the same rules.
3rd Level Druid Example:
A 3rd level druid can prepare four spells and cast four 1st level spells and two 2nd level spells after a long rest.
In the morning after a long rest you choose to prepare three of the four spells you can have prepared. You prepare Cure Wounds (1st level), Animal Friendship (1st level) and Moonbeam (2nd level). During the day you get into an encounter and cast Moonbeam(2nd level) and Cure Wound(1st level) twice. Now you have used two of your four 1st level spells and one of your two 2nd level spells. You can still cast two more of the 1st level spells you have prepared and one more of the 2nd level spells you have prepared before you need to take a long rest to cast any more spells. Now as you only prepared three of the four possible prepared spells in the morning you can take a few minutes to prepare the last one at anytime during the day. After the encounter you find a cave entrance and realize you want to use the spell Darkvision (2nd level). You take a few minutes to prepare Darkvision spell and add it to your prepared spells (Cure Wounds(1st), Animal Friendship(1st), Moonbeam(2nd) and Darkvision(2nd)). Now you can cast Darkvision or Moonbeam with your remaining 2nd level spell for the day.
Any spell with Ritual in the description can be cast as a ritual which increases the casting time by ten minutes but does not expend a spell use for the day as follows:
Bard – The spell must be one of the characters Known Spells.
Cleric/Druid – The spell must be prepared.
Mage – The spell must be in the Mage’s Spellbook.
Paladin – Paladins cannot cast spells as a Ritual.
Ranger – Rangers cannot cast spells as a Ritual.
To continue the example, after casting Darkvision and going into the cave you get in another fight and get wounded. You cast Cure Wounds twice to heal your wounds. You have now cast four 1st level spells and two 2nd level spells depleting all your spells for the day. However because you have Animal Friendship prepared and it is a Ritual Spell you can still cast it without any spells left for the day. You just have to cast it as a Ritual which will take an extra 10 minutes. If you had only used 1 Cure Wounds in the cave so you had only cast three of your four 1st level spells for the day you could cast Animal Friendship as your last 1st level spell and it would not take ten minutes, only the standard time but then you would have used your last remaining 1st level spell for the day.
Cantrips work the same as normal spells except in the following ways:
Cantrip Spell List:
You select a few cantrips during the character creation(probably 2-4 depending on your class) and might add more as you advance in levels.
Paladins and Rangers do not have any cantrips.
You don’t prepare cantrips, all the cantrips on your spell list are always prepared.
In the default rules you can cast an unlimited number of cantrips per day. However I have changed this to be twice the number of first level spells you can cast. So for a 3rd level druid you can cast 8 cantrips per day.
Bard and Paladin – Charisma
Cleric, Druid and Ranger – Wisdom
Mage – Intelligence
Saving Throw DC:
The DC to resist one of your spells equals 8 + your Magic Ability modifier. If you are holding or displaying a spellcasting focus(see class descriptions) when you cast a spell, add your proficiency bonus to the spell’s saving throw DC.
Rangers are an exception, they never add their proficiency bonus to their spell’s saving throw DC.