Does casting Light, or a similar spell, have any effect when the caster is swallowed by a monster?

Question

So you've been swallowed by a Giant Toad. Oops. Your fellows are sure to kill it soon enough, but you want to do something in the meantime.

"Well," you say, "perhaps I'll attack the toad from the inside!"

"Ah," says God (you're used to God commenting on your intended actions), "But remember, you're blinded and restrained. So any roll you make is with Disadvantage." (You are also used to God using bizarre terminology to describe your life like some sort of game. You roll with it.)

"But I am surrounded on all sides by toad! Surely that would involve some advantageous modifier!"

"You are restrained by the toad's gullet," replies God, "your arms can't move well enough to attack effectively, even if you weren't blind."

Phooey. You think to yourself for a moment. "Perhaps I'd better cast a spell, then," you say, "Magic Missile doesn't even require an attack roll! Oh, but, drat, I need to see the target, don't I? Perhaps I should cast Light on any given object on my person first."

"It's not just dark, you're blinded," says God, "Light will do nothing. Neither will torches, lanterns or whatnot."

"Are you suggesting that my face is always pressed up against some portion of the frog's anatomy? Restrained or not, it feels like I should have at least the range of motion to remedy that!"

So, is there any indication whatsoever that you can ever see the toad that you are inside of enough to target it with a spell?

Answer 1

No, your "god" was right.

As the giant toad's stat block clearly states:

The swallowed target is blinded and restrained, ...

This means you can't regain your vision by creating light inside of the toad. A blind man with a torch in front of his face is still a blind man.

Note that a spell like Darkness never gives any indication of the "blinded" condition:

Darkness spreads to fill a 15-foot-radius sphere for the duration. The darkness goes around corners. A creature with darkvision can't see through this darkness, and nonmagical light can't illuminate it.

This means the effect of the spell can be ended with a powerful enough source of light.

You could bargain with your god and make a clear agreement on how your table is going to handle this issue in the future, but bear in mind that they are technically correct.

Answer 2

From a thematic perspective, do note that they are likely bathing in digestive juices. Opening your eyes would probably result in an ACTUAL permanent blinding if you were a human being and not a game piece.

So, if you wish to override gameplay with reality, you are still blind.

However, as a DM, if a player were in this situation and needed a hit roll on a spell without somatic, verbal, material components, that described itself as a ray that makes contact, I might consider the to-hit roll being 'not hitting yourself' and give no penalty or advantage.

This would be a thematically appropriate time to inflict a concentration check as well for any spell of any type to even cast it.