Sorry, Thaum, but I can't affirm you on this one.![]()

mach1.9pants said:But really if you can make an attack with a bow or sword, then you can cast spells. Heck you can use a sling!
A character with 5 levels of exhaustion (next to death) has disadvantage on ability checks, attack rolls and saving throws; has their hit point maximum halved and their speed reduced to 0; and yet suffers no appreciable penalty to spellcasting or concentration.
It's a good question though. Would this be different if the caster is in manacles? a completely mundane item, arguably more constraining that the effects of a web spell: are manacles sufficient to prevent somatic components? Possibly so: I note that the knock spell does not need somatic components.
As for the original OP, and my adhoc solution to most of this, would be to use the Con-check concentration mechanic to cast spells in greatly impaired circumstances. On a failure, you lose your action, but don't expend the spell slot.
I'm really intrigued by this question. Manacles are easier to wrap our heads around, because they are real things that really restrain people. Manacles "restrain", so, for consistency, should have the same ruling as web. Yet they do seem different.
If I'd remembered concentration at the time, I might have done this.
Part of the meta-story of this is that my wonderful wife had worked a 16 hour day, but wanted to play the climactic scenes of the adventure. She has previously told me, on numerous occasions, rules discussions put her to sleep. So I made a call without taking the time to look at the puzzle from 15 angles. And I told the group we'd revisit the question.
Thaumaturge.
Depends on whether manacles do hands and/or feet, I guess depends on the type.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.