Contingency and concentration

[Blit_Wizbok]

If Contingency is used to produce a spell that requires concentration, does the spellcaster have to concentrate on said spell when Contingency triggers? Or does it work like Glyph of Warding, where concentration isn't required?

[RSP]

RAW you would need to maintain concentration on the contingent spell at the casting of Contingency as that is technically when the contingent spell is cast and the Contingency spell doesn't give any exception to the normal Concentration rules:

"You cast that spell–called the contingent spell–as part of casting contingency, expending spell slots for both, but the contingent spell doesn’t come into effect."

However, I'd probably rule it as Concentration is required only after the spell takes effect.

[GoodbyeSoberDay]

By RAW, it depends on how you define "come into effect" and its implications. IMO the simplest reading is that, if a spell hasn't come into effect, neither have its descriptors, one of which is the "Duration" line, which includes the (Concentration) tag. This would help explain how a 10 day contingency is actually able to allow Water Breathing to be contingent at all.

RAI, it's clearly as Rsp29a would rule, and how I would interpret RAW. Treat the contingent spell as "cast" once it "comes into effect," which means you have to maintain concentration as it comes into effect, because you did in fact cast the spell.