D&D Spells and Spell Slots Explained for Beginners

In D&D-style games, a caster has two kinds of magic: cantrips, which can be cast as often as you like, and leveled spells, which each use up a spell slot. Spell slots are daily charges that come back after a long rest. A spell either asks you to make a spell attack roll against the target's Armor Class, or asks the target to make a saving throw against your spell save DC. Some spells need concentration, which you can hold on only one spell at a time. That is most of what a new player needs. This guide explains each piece in plain words, with the arithmetic, and then shows honestly how Thavernia's AI Game Master handles magic, which is much simpler.

The short answer#

• Cantrips are free. Cast them every turn if you like; they never run out.
• Leveled spells cost slots. A 1st-level spell uses a 1st-level slot (or higher). A level 1 full caster has two.
• Slots come back on a long rest. Warlocks are the exception: theirs come back on a short rest.
• Spell attack: d20 + proficiency bonus + casting ability modifier, against Armor Class.
• Spell save DC: 8 + proficiency bonus + casting ability modifier; the target rolls to resist.
• Concentration: one such spell at a time; damage can break it.
• Components: say the words, make the gestures, hold a focus or pouch for the materials.

Cantrips vs leveled spells#

Every spell has a level from 0 to 9. Level 0 spells are called cantrips. They are simple tricks a caster has practised so often that they cost nothing: a bolt of fire, a spark of light, a mocking word with a sting. You can cast a cantrip every turn for the whole adventure.

Spells of level 1 to 9 are leveled spells. They do more: heal a dying friend, put a room of guards to sleep, throw a ball of fire. Each casting uses a spell slot. A spell's level is not the same as your character's level: a level 5 Wizard can cast 3rd-level spells, and only a very high-level character reaches 9th-level spells.

Spell slots, explained simply#

Think of spell slots as charges in a battery, sorted by size. Small charges power small spells, big charges power big ones, and a big charge can always power a small spell. When the charges are spent, you are down to cantrips until you rest.

The number of slots depends on your class and level. Full casters (Bard, Cleric, Druid, Sorcerer, Wizard) all follow the same table at low levels:

• Half casters (Paladin, Ranger) get fewer slots, and the highest spell level they reach is 5th.
• Warlocks use pact magic: very few slots (one at level 1, two from level 2), all of the same level, and they come back on a short rest instead of a long one.
• Upcasting. You may cast a spell using a higher slot than it needs. Many spells say what improves when you do, such as an extra die of damage or one more target.
• One slotted spell per turn, as a rule of thumb. The exact rule about casting a second spell with a bonus action differs between the 2014 rules and the 2024 revision; ask your Game Master if it comes up.

Spell attack and spell save DC#

Each casting class uses one ability for its magic, called the spellcasting ability. It sets how accurate and how hard to resist your spells are.

A spell resolves in one of two ways, and the spell's description tells you which:

• Spell attack roll. You roll, like a weapon attack. Roll a d20 and add your spell attack bonus (proficiency bonus + spellcasting ability modifier). Meet or beat the target's Armor Class and the spell hits. A natural 20 is a critical hit.
• Saving throw. The target rolls to resist. They roll a d20 plus their own modifier for the ability the spell names (Dexterity to dodge a blast, Wisdom to resist a charm), against your spell save DC (8 + proficiency bonus + spellcasting ability modifier). Many damaging spells still deal half damage on a successful save.

Casting ability score 16 -> modifier +3
Proficiency bonus at level 1 = +2

Spell attack bonus = 2 + 3      = +5  (roll d20 + 5 vs Armor Class)
Spell save DC      = 8 + 2 + 3  = 13  (the target must roll 13 or more)

How a d20 check, Armor Class and advantage work in general is explained in D&D dice and checks explained.

Concentration#

Some spells last for a while and need you to keep focusing on them: a protective blessing, a wall of fire, a creature held in place. Their description says concentration. Three rules cover almost every case:

• One at a time. If you start a second concentration spell, the first ends immediately.
• Damage can break it. Each time you take damage, make a Constitution saving throw. The DC is 10 or half the damage taken, whichever is higher. Fail and the spell ends.
• Being knocked out ends it. So does dying, and so does choosing to drop the spell, which you can do at any time.

Components in plain words#

Each spell lists what you need to cast it, abbreviated as V, S and M:

• V (verbal): you must speak. A gagged caster, or one inside magical silence, cannot cast these.
• S (somatic): you must gesture with at least one free hand.
• M (material): you need a physical item. A component pouch or a spellcasting focus (a wand, a staff, a holy symbol, a druidic sprig, depending on class) covers any material without a listed price.
• Costly materials are real. If a spell names a price, such as a diamond worth a set amount of gold, you must actually own it, and if the spell says it is consumed, it is gone after the casting.

Preparing vs knowing spells#

Casters do not have access to every spell at once. There are two ways a class decides what you can cast today:

• Preparing. You choose a set of spells from a larger list each day, usually after a long rest. Clerics and Druids prepare from their whole class list; Wizards prepare from the spells written in their spellbook; Paladins prepare too.
• Knowing. In the original 5e rules, Bards, Sorcerers, Warlocks and Rangers know a short fixed list and can only swap a spell when they level up.
• The 2024 revision calls every caster's list "prepared", but how often you can swap still differs by class. Either way, your daily list is limited.
• Slots are shared. Preparing a spell does not use it. You prepare, say, five spells, and then spend your two slots on whichever of those five you need.

Rituals are a useful extra: some utility spells carry a ritual tag and can be cast without a slot if you take ten extra minutes. Which casters can do this, and from which list, depends on the class.

Rests: getting your magic back#

This is why pacing matters. A Wizard who spends both slots in the first fight of the day casts only cantrips for the rest of it. Many Game Masters plan several encounters between long rests precisely so that choosing when to spend a slot is a real decision.

Common beginner mistakes#

• Spending every slot in the first fight. Keep at least one slot for an emergency, usually healing or an escape.
• Forgetting cantrips exist. A damage cantrip every turn is often better than nothing while you wait for the right moment.
• Stacking concentration spells. The second one ends the first. Check the spell before casting it.
• Standing in the front line with a concentration spell. Every hit is a chance to lose it.
• Confusing spell level with character level. A level 3 character casts 1st and 2nd-level spells, not 3rd.
• Forgetting upcasting. Your leftover 2nd-level slot can power a stronger version of a 1st-level spell.
• Preparing only damage spells. Utility spells (light, detection, speaking with others, getting past obstacles) solve problems that fire cannot.
• Reading every spell in the list. Learn the four or five you have prepared. That is enough for a first session.

How magic works in Thavernia#

Thavernia is a fantasy tabletop RPG run by an AI Game Master, with simplified 5e-style rules. Its magic keeps the parts that make spells exciting (a d20 roll on your casting ability, a big spell that has to be timed) and drops the bookkeeping. There are no spell slots, no spell lists to prepare and no components to track. Here is what actually happens.

Outside combat: describe it, roll it

You write what your hero does, magic included: "I whisper a ward over the door", "I call light into my staff and search the crypt". A referee step decides whether the action needs a roll, and for a spell or magical effect it uses your class's casting ability: Intelligence for a Wizard, Wisdom for a Cleric, Druid or Ranger, Charisma for a Bard, Sorcerer, Warlock or Paladin. It sets a difficulty that leans low for routine actions, the server rolls the d20, you throw it on screen, and the Game Master narrates the result it has to honour.

In combat: the class action kit

On the default tactical map, each class has four kit actions plus three shared ones (Attack, Defend, Help). For casters, most of the kit is spells. Instead of slots, actions cost action points (AP) that refresh every round: casters have 2 AP per round, plus 1 at level 5 and 1 more at level 9. The strongest actions also have a cooldown: after use, they wait one to three rounds before they can be used again.

• The cantrip feel. The first action in each row costs 1 AP and has no cooldown, so you can use it every round, much like a damage cantrip.
• The big-spell feel. The area spells (Fireball, Lightning Bolt, Hunger of the Void, Call Lightning, Spirit Guardians, Hypnotic Pattern) cost 2 AP, unlock at level 5 and wait 3 rounds after use. Timing them is the decision a slot would have been.
• Rolling the spell. The caster always rolls: a d20 plus the casting ability modifier against a difficulty the referee sets. There is no separate spell save DC for enemies to roll against.
• Damage on the action. Each damaging action shows its damage range. Your casting ability and your level raise it, a higher d20 lands higher in the range, a natural 20 goes past the top, and a miss deals nothing.
• Range and cover. Ranged spells work at any distance on the board, but the difficulty rises by 2 when an enemy is standing next to the caster, and by 2 when the target is in cover. Casters still want to stay back.
• Buffs are tracked by the server. When a blessing such as Bless lands, the server gives the target advantage for a set number of rounds; nobody has to remember it.

Focus and making camp

Once per combat every hero can press Focus, the class signature move: the hero's next dice roll with advantage and the narration stages the class's own move (Arcane Overload for a Wizard, Holy Light for a Cleric, Eldritch Pact for a Warlock). Focus is not the same as 5e concentration; it is a once-per-fight boost. It recharges when the fight ends or when the group makes camp.

Camp is Thavernia's rest. The host can make camp outside combat when no fresh threat is near, at most once every six Game Master turns. Every hero recovers half of the hit points they are missing (rounded up), lasting conditions such as poison or burning are cleared, and Focus is recharged. There are no slots to refill, because there are none.

A campaign can also be set to narrative combat, with no map. Then there are no kit buttons: you describe your spell in your own words and it is rolled on your casting ability, as outside combat.

Where Thavernia simplifies#

Cast your first spell#

The trial needs no account and no card: start with a ready-made hero or create a caster of your own, and play three turns as a guest. A free account gives you 20 turns. If you are still choosing a class, which D&D class to pick as a beginner compares all twelve, and how to make a D&D character walks through the rest of the sheet.

Frequently asked questions#