The rules do not specify that
• You are trying to climb a steep or slippery cliff, avoid hazards while climbing a wall or hanging on a surface while something is trying to knock you out. (Basic rules page 62)
The PC starts a capacity test when the DM calls one.
A abilities check tests the innate talent and drive of a character or monster to meet a challenge. The DM requests a capacity check when a character or monster attempts an action (other than an attack) that has a risk of failure.
When the outcome is uncertain, the dice determine the results. Basic rules p. 61
Checks of aptitude, if you are the SM: run once (recommendation)
Depending on how our games have been played over the last 5 years, I recommend the following if you are a DM:
For a climb, check once and consider the place as "halfway up"
Halfway up or down, this simplifies the importance (and even if) of the damage due to the fall.
Exception to the general recommendation: if something changes the conditions to make it more difficult. If during the climb, for example, a rock slide begins,
or a huge volume of water is released and interferes with climbing –
conditions that were not present at the beginning – a new audit to manage
this change is an option.
- If you call for a turn each turn, you will eventually fail. It's a little penal for the player to do it.
Climbing in general costs half the movement
Climbing, swimming and crawling
Each movement foot costs 1 extra foot (2 extra feet in difficult conditions).
terrain) when climbing, swimming or crawling. You do not know that
additional fees if you have a climb speed and use it to climb or
swimming speed and use it to swim. At the choice of DM, climb on a
slippery vertical surface or with few handles requires a
successful verification of strength (athletics). (Basic rules, page 67)
Many climbs do not require any capacity / capacity checks. (It is very easy to climb a lot of trees). This is only in case the climb is unaided, or has a chance of failing, as the assignment of a domain controller and the call to a throw is required. (Some trees are all trunks up to about 30: without special tools, they are hard to climb)
References for more information: DMG p. 237-238; 245