I was wondering if spells like Shield wizard spell could be used as an action instead of as a reaction in response to some trigger? Shield spell gives protection until the start of casters next turn, so would it be within the rules to cast it as an action in my turn?
[RPG] Can reaction spells be used as an action
dnd-5ereactionsspellswizard
Best Answer
No.
If the casting time of a spell is 1 reaction, you can only cast it using your reaction (unless you benefit from a special feature that lets you do otherwise). This is because there is no general rule that lets you change the casting time of a spell from 1 reaction to 1 action.
There's nothing I can cite that confirms that because it's impossible to prove a negative. Rather, there simply isn't a general rule that would let you do what you're asking for.
However, this prohibition is heavily implied by the rules for casting times and for reaction spells (see PHB p. 202, emphasis mine):
So when the casting time of a spell is "1 reaction," you are required to use your reaction to cast it in response to the exact event or timing indicated in the spell's description. You can't choose to cast it in another fashion (again, unless you benefit from some special feature that lets you do so).