Does climbing in combat require an action?

[Sir-Carlos]

Example: A fight in an alley. One character wants to climb to the top of a building via a rain gutter. He needs to make an athletics check for that.

The question is: Does that count as an action? Or is it just a part of his movement? I couldn’t find an answer in the rule book.

[Snails]

If it is very easy to Climb with good handholds, then the default rule is half speed and no check required. So, you might want to use an Action if you have more than 15 feet to scale.

It is not logically required that an Action be required for locomotion over difficult terrain features.

In this case, if I were DM I would give you two different DCs. An easy one if you use an Action and really putting concentration and effort into it, and a more difficult one if you are hurrying you way up.

[Dr.Samurai]

Climbing is a type of movement, so you can do it as part of your movement. Your action is still available to you.

[stoutstien]

Example: A fight in an alley. One character wants to climb to the top of a building via a rain gutter. He needs to make an athletics check for that.

The question is: Does that count as an action? Or is it just a part of his movement? I couldn’t find an answer in the rule book.
Generally climbing doesn't take an action or requires any checks. (PG ~182 PHB. Special types of movement)
I'd say no check and no action required if they have both hands free. If they only have one hand or if the weather is bad then an athletic check would be warranted but it would be no more than 10.

Special note that climbing uses the 2:1 ratio for movement cost that could potentially stack with difficult terrain meaning it takes 3 feet of movement for every foot transverse.

For strength based PCs jumping can work better than climbing.

[BoutsofInsanity]

So it doesn't require an action.

What it would read as mechanically

Object - Alley Wall - Persistent Effect - Should anyone without a climb speed attempt to climb this wall without assistance (Like items) they must make a strength (athletics) check DC XX as part of their movement. If they fail they immediately fall to the bottom of the wall.

The character is making a check as part of their movement to climb the wall if the wall warrants having a check to determine if it can be climbed.

This is different from a say the following

Object - Perfect Climbing Tree - Persistent effect - A tree exceptionally prone for climbing. The handholds are easy to grasp and branches sturdy for any weight. Any character can climb this tree as part of their movement.

In this instance, the inherent properties of the space and object are forcing a climb check on the player, when normally one wouldn't be required. We as Dungeon Masters do this calculation in our head by applying description and improvising narratives within the game space. We don't "Mechanically describe every object in the game" before the players sit down. We perform these calculations in our heads as the game plays based around what we think is best.

Compare that to something that might require an action to climb.

Object - Inverted Climbing Wall - Persistent Effect - A dangerous wall that tilts forward causing characters who climb it without assistance to have to take an action and perform an Athletics (Wisdom) DC12 check to determine where to place their hands and feet to continue climbing. Those that don't can only move forward at 1/4th movement penalty. That's where the players would be forced to take an action to continue climbing.

[JLandan]

Example: A fight in an alley. One character wants to climb to the top of a building via a rain gutter. He needs to make an athletics check for that.

The question is: Does that count as an action? Or is it just a part of his movement? I couldn’t find an answer in the rule book.

It is just part of the movement. However, if the regular movement is not enough to get to the top, you have the option of the Dash action, which gives you more movement but uses your action.

Whether or not a Strength (Athletics) check is required and what DC it would be is entirely a DM call.

[Telok]

Example: A fight in an alley. One character wants to climb to the top of a building via a rain gutter. He needs to make an athletics check for that.

The question is: Does that count as an action? Or is it just a part of his movement? I couldn’t find an answer in the rule book.

Every game I've played in, yes. Rulings not rules ftw.

[Jervis]

Generally climbing doesn't take an action or requires any checks. (PG ~182 PHB. Special types of movement)
I'd say no check and no action required if they have both hands free. If they only have one hand or if the weather is bad then an athletic check would be warranted but it would be no more than 10.

Special note that climbing uses the 2:1 ratio for movement cost that could potentially stack with difficult terrain meaning it takes 3 feet of movement for every foot transverse.

For strength based PCs jumping can work better than climbing.

Isn't "super difficult terrain" or whatever the AL modules call it 4 feet per foot of movement? I forget which module uses that.

[stoutstien]

Isn't "super difficult terrain" or whatever the AL modules call it 4 feet per foot of movement? I forget which module uses that.

Some spell and effects have 1:4,1:3,1:2, or a flat reduction that isn't DT but the general rule for climbing is 1:2 and difficult terrain while climbing calls for 1:3. It should be 1:4 honestly and that's what I use most of the time.

[ImproperJustice]

Climbing is part of their movement. Typically a player climbs at half their movement speed.

A Rogue’s dash or Monk’s speed + Step of the Wind helps them clear walls / obstacles quickly.

The Thief Subclass, Tabaxi Claws, Ranger Feature, and Athlete Feat all grab climb speeds which allow for full movement when climbing, and can often times provide some interesting tactical options in combat, especially when grappling.

[Kane0]

Climbing is part of their movement. Typically a player climbs at half their movement speed.

A Rogue’s dash or Monk’s speed + Step of the Wind helps them clear walls / obstacles quickly.

The Thief Subclass, Tabaxi Claws, Ranger Feature, and Athlete Feat all grab climb speeds which allow for full movement when climbing, and can often times provide some interesting tactical options in combat, especially when grappling.

Dont forget the Spider Climb spell of course, and things like Druid Wildshape or the polymorph spell which can turn someone into a creature with a climb speed. I think there is a barbarian that gets a climb feature somewhere too?

[Skrum]

Be the second coolest race, Dhampir, and just run up the wall.

Yeah what everyone else said. Climbing is part of your move. Often times though people end up using their action to dash b/c climbing is slow.

[Keravath]

In general, climbing is part of your move. However, a DM can rule that any particular climbing situation requires more attention so it would take your action.

If a creature has a climb speed then on a surface with good hand/foot holds they could usually move up it without the DM requiring a check. The general rule is that for creatures without a climb speed, climbing costs an extra 1' of movement for each 1' move.

However, a DM adjudicates every situation and they are unique.

Is a character climbing an alley wall with no one around the same as a character climbing an alley wall in the midst of combat?
What kind of hand and foot holds are available? If the wall is cinder block with mortared gaps then it might be a very different climbing experience from natural stones mortared together, bricks, wood or siding. Even climbing a drain spout could be an issue - the hand holds might be good but these things are usually not intended to support the weight of a character holding onto the downspout.

All of these factors could cause a DM to:
1) Ask for a check - likely Athletics - DC depending on circumstances.
2) Decide that the surface is difficult enough to climb that it would take your action. (I'd usually say that this is a bit much since climbing is included as a part of movement .. but a DM could decide otherwise and I wouldn't argue with them during the session but I might ask to discuss it in private afterward).
3) Decide that climbing could give attackers advantage because the climbing character can not look around to watch for attacks and can not dodge or move out of the way of an incoming attack the way they could if they were on the ground. (A DM is explicitly allowed in the rules to decide when circumstances might impose advantage and disadvantage so this isn't necessarily a "house rule").

Relevant rules:

"Climbing, Swimming, and Crawling

Each foot of movement costs 1 extra foot (2 extra feet in difficult terrain) when you’re climbing, swimming, or crawling. You ignore this extra cost if you have a climbing speed and use it to climb or a swimming speed and use it to swim. At the DM’s option, climbing a slippery vertical surface or one with few handholds requires a successful Strength (Athletics) check. Similarly, gaining any distance in rough water might require a successful Strength (Athletics) check."

"Movement and Position

In combat, characters and monsters are in constant motion, often using movement and position to gain the upper hand.

On your turn, you can move a distance up to your speed. You can use as much or as little of your speed as you like on your turn, following the rules here.

Your movement can include jumping, climbing, and swimming. These different modes of movement can be combined with walking, or they can constitute your entire move. However you're moving, you deduct the distance of each part of your move from your speed until it is used up or until you are done moving."

"The DM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result."