Attacking through a barred forcecage

I've always assumed that the intent of the barred cage type forcecage is to allow trapping a creature while still being able to attack it, but I was just thinking about it and realized there's a problem: the vast majority of attacks will not, in fact, be able to fit through half inch gaps, or will have very poor odds, and given that a half inch gap will stop gases in D&D (gaseous form) there's an argument for it even stopping more diffuse damaging effects, or at least granting cover.

The spell, naturally, is entirely silent on how difficult it is to attack through. So... thoughts?

Personally, I would say that attacking through it with weapons is impossible. The odds of being able to get any weapon, even ammunition from a ranged weapon, through the gaps with any force behind them is infinitesimal. Even the tip on an arrow would be wider than the gap. 

I could see the argument that it is POSSIBLE, though unlikely, so at the very least I would impose a minimum of half cover and disadvantage on any attack through the bars. An AoE effect I would have to evaluate on a case-by-case basis. For example, I would say Ice Storm is completely blocked but Sickening Radiance isn't.

IMO, the gap is too small for any weapon or your Unarmed Strike (I know, Rules Aren't Physics) to reach a creature, but technically, if you rule it doesn't have Total Cover (this would be my ruling), you could target it with a ranged spell.

Also, following that ruling, an area of effect should technically affect the creature:

[...] An area of effect has a point of origin, a location from which the effect’s energy erupts. The rules for each shape specify how to position its point of origin. If all straight lines extending from the point of origin to a location in the area of effect are blocked, that location isn’t included in the area of effect. To block a line, an obstruction must provide Total Cover.See also “Cover.”

 
Anyway, I think this is DM's territory. Maybe a DM could consider that the cage provides Total Cover to simplify the interactions with spells or tiny ammunition. 

EDIT: for clarity.

Stabbing a sword through the gaps should work, but that would probably count as an improvised weapon unless you're using a rapier or similar. And I think normal gasses should fit through.

Am I crazy, or does Gaseous Form not say anything about a half-inch gap stopping movement? The version you linked states: "The target can pass through narrow openings, but it treats liquids as though they were solid surfaces."

Also, I would suggest that if a 1/2 inch gap did prevent someone in Gaseous Form from being able to move through a space, that doesn't mean all gasses behave the same way. Being in a gaseous form still means you are a singular sentient being held somewhat together by magical forces. This would be different than a fog or some poisonous gas or whatever. So I would rule that gasses would be able to go through the bars.

From the description, I would say the "cage" version of the Forcecage spell provides three-quarters cover. "An object that covers at least three-quarters of the target." I don't think it would offer Total Cover because the entire target isn't covered. Therefor the creature in the cage would get "+5 bonus to AC and Dexterity saving throws" (as would any creatures outside of the spell that are targeted by the creature inside). 

I think this makes sense because of the description of the "box" version of the spell. "A prison in the shape of a box can be up to 10 feet on a side, creating a solid barrier that prevents any matter from passing through it and blocking any spells cast into or out from the area." If the cage version also provided total cover, then spells wouldn't be able to be cast in or out from that as well. So it seems to suggest the cage version does not provide total cover. 

I can see someone with a longsword being able to slide the blade through the gap in the bars and thrust at the target, but in this instance it would have +5 to their AC for being behind 3/4 cover. 

Some weapons, such as a Blowgun could fire a Needles through a Forcecage  made from 1/2-inch diameter bars spaced 1/2 inch apart, so can spells still having A Clear Path to the Target.

If you want to to create a solid barrier that prevents any matter from passing through it and blocking any spells cast into or out from the area, you must a prison in the shape of a box instead. 

Quote from Pantagruel666 >>

I've always assumed that the intent of the barred cage type forcecage is to allow trapping a creature while still being able to attack it, but I was just thinking about it and realized there's a problem: the vast majority of attacks will not, in fact, be able to fit through half inch gaps, or will have very poor odds, and given that a half inch gap will stop gases in D&D (gaseous form) there's an argument for it even stopping more diffuse damaging effects, or at least granting cover.

The spell, naturally, is entirely silent on how difficult it is to attack through. So... thoughts?

 After reading the spell, I would assume that the purpose is to trap and NOT allow you to attack it. The duration might imply this as well as the general body of the spell that provides no real tips on how to circumvent the barrier in a meaningful way.

Quote from MaximusArael020 >>

Am I crazy, or does Gaseous Form not say anything about a half-inch gap stopping movement? The version you linked states: "The target can pass through narrow openings, but it treats liquids as though they were solid surfaces." 

For the purposes of Forcecage specifically, Gaseous Form wouldn't help you escape, as the description of Forcecage specifically states "A creature inside can't leave [the cage] by nonmagical means." And while Gaseous Form is a magical spell, once cast, you would use mundane means to leave the cage. That said, gases could certainly enter and exit the spell, and, ironically, a gaseous creature (such as a Wizard using Gaseous Form) could enter the cage. They just couldn't leave, except through some means such as Teleport, which would require a Charisma save.

Quote from RWinnie >>

Quote from MaximusArael020 >>

Am I crazy, or does Gaseous Form not say anything about a half-inch gap stopping movement? The version you linked states: "The target can pass through narrow openings, but it treats liquids as though they were solid surfaces." 

For the purposes of Forcecage specifically, Gaseous Form wouldn't help you escape, as the description of Forcecage specifically states "A creature inside can't leave [the cage] by nonmagical means." And while Gaseous Form is a magical spell, once cast, you would use mundane means to leave the cage. That said, gases could certainly enter and exit the spell, and, ironically, a gaseous creature (such as a Wizard using Gaseous Form) could enter the cage. They just couldn't leave, except through some means such as Teleport, which would require a Charisma save.

 I completely agree with your statement. 

I was responding to this portion of the OP:

...and given that a half inch gap will stop gases in D&D (gaseous form) there's an argument for it even stopping more diffuse damaging effects, or at least granting cover.

I thought I saw the same 1" figure for gaseous form as most oozes and the like have, but it doesn't, so I have no idea where I hallucinated that from.

I mean from a rules as written point of view a creature in the cage option for forcecage would only provide half cover. Based on the description of cover in the combat section of the player's handbook half cover is granted when half of the target is covered by another creature or object and 3/4 cover requires 3/4 of the creature covered by specifically an object. Since this would literally block have of the area of the creature it should be half cover and wouldn't qualify for 3/4 cover. I don't think I'd rule that as a DM but that's what the player's handbook says. For most spells I don't see a reason to deviate from that ruling. As a DM though I'd definitely rule that most physical attacks can't reach the target.

Quote from MeatLuggin >>

I mean from a rules as written point of view a creature in the cage option for forcecage would only provide half cover. Based on the description of cover in the combat section of the player's handbook half cover is granted when half of the target is covered by another creature or object and 3/4 cover requires 3/4 of the creature covered by specifically an object. Since this would literally block have of the area of the creature it should be half cover and wouldn't qualify for 3/4 cover. I don't think I'd rule that as a DM but that's what the player's handbook says. For most spells I don't see a reason to deviate from that ruling. As a DM though I'd definitely rule that most physical attacks can't reach the target.

 That would depend on the arrangement of the bars. It is not specified if the bars are only in one direction, or a bi-directional grid. If they run vertically and horizontally, they would grant ¾ cover as each 1in² would have ¾in² of bars.