Cantrips seem to be the only type of spell that cares only about your class level.
However, in the multiclassing section they are not mentioned, does this mean that cantrips use your character level, instead of your class level?
Does this mean a Warlock 2 / Fighter 15 can cast an Eldritch Blast with 4 beams just like a level 17 Warlock?
While it never explicitly states this anywhere in basic or the PHB, it only states the level at which the cantrip increases in power. One of the design goals of 5e and one of the things it imported from 4e was that there should never be a time where a magic user is forced to resort to making a weapon attack that they are ill-suited for. Cantrips act like 4e's At-Will spells and as such level with each "tier" in 5e to maintain their usefulness. Tying this to character level means that players who multiclass or for example start off with a free cantrip (such as High Elves) are still able to make use of those cantrips throughout the whole of the game.
A clarification was added to the Sage Advice Compendium.
Cantrips
If a character has levels in more than one class, do the character’s cantrips scale with character level or with the level in a spellcasting class?
Cantrips scale with character level. For example, a barbarian 2 / cleric 3 casts sacred flame as a 5th-level character. (Sage Advice Compendium V_2.0; page 11)
Later, this was added to the rules for multiclass spellcasters (PHB, p. 164) in the Player's Handbook errata:
If a cantrip of yours increases in power at higher levels, the increase is based on your character level, not your level in a particular class.
Per a Twitter post by Jeremy Crawford (Designer/Editor of D&D 5e):
A multiclass character uses character level to determine the damage of a cantrip.
This was added to the Sage Advice Compendium (page 4) as of its initial release in 2015:
If a character has levels in more than one class, do the character’s cantrips scale with character level or with the level in a spellcasting class?
Cantrips scale with character level. For example, a barbarian 2 / cleric 3 casts sacred flame as a 5th-level character.
Character level. This is straight from the design team (via Sage Advice D&D).
Eldritch blast scales with character level, not warlock level. This is true of any cantrip that scales with level.
This was added to the Sage Advice Compendium.
Cantrips
If a character has levels in more than one class, do the character’s cantrips scale with character level or with the level in a spellcasting class? Cantrips scale with character level. For example, a barbarian 2 / cleric 3 casts sacred flame as a 5th-level character. (Sage Advice Compendium V_2.0; page 11)
Cantrips
If a character has levels in more than one class, do the character’s cantrips scale with character level or with the level in a spellcasting class? Cantrips scale with character level. For example, a barbarian 2 / cleric 3 casts sacred flame as a 5th-level character. (Sage Advice Compendium V_2.0; page 11)
This is copied right from sage advice compendium.
I saw a tweet from Mike Mearls that addresses this, Cantrips are intended to use your character level. The example give I believe was a lvl 20 high elf barbarian being able to cast firebolt at max level. The spells refer generally to character level and not spell caster level.
The Sage Advice Compendium confirmed this when it was published.
