A tool helps you to do something you couldn't otherwise do, such as craft or repair an item, forge a document, or pick a lock. Your Ancestry, Class, Background, or Feats might give you Proficiency with certain tools. Proficiency with a tool allows you to add your proficiency bonus to any d20 Test you make using that tool. Tool use is not tied to a single Ability Score, since Proficiency with a tool represents broader knowledge of its use. For example, the DM might ask you to make a Dexterity Test to carve a fine detail with your woodcarver’s tools, or a Strength Test to make something out of particularly hard wood.
Tool proficiencies are a useful way to highlight a character's background and talents. At the game table, though, the use of tools sometimes overlaps with the use of skills, and it can be unclear how to use them together in certain situations. The following section and pages offer various ways that tools can be used in the game.
Tools have more specific applications than skills. The History skill applies to any event in the past. A tool such as a Forgery Kit is used to make fake objects and little else. Thus, why would a character who has the opportunity to acquire one or the other want to gain a tool proficiency instead of proficiency in a skill?
To make tool proficiencies more attractive choices for the characters, we can employ the following rules, outlined below:
Advantage. If the use of a tool and the use of a skill both apply to a Test, and a character is proficient with the tool and the skill, consider allowing the character to make the Test with Advantage. This simple benefit can go a long way toward encouraging players to pick up tool proficiencies. In the tool descriptions that follow, this benefit is often expressed as additional insight (or something similar), which translates into an increased chance that the Test will be a success.
Added Benefit. In addition, consider giving characters who have both a relevant skill and a relevant tool proficiency an added benefit on a successful test. This benefit might be in the form of more detailed information or could simulate the effect of a different sort of successful Test. For example, a character proficient with mason's tools makes a successful Wisdom (Perception) Test to find a secret door in a stone wall. Not only does the character notice the door's presence, but you decide that the tool proficiency entitles the character to an automatic success on an Intelligence (Investigation) Test to determine how to open the door.