Because of Tool's experimental approach to music, it is disputed how to define their place in reference to traditional musical genres. Tool is inarguably a part of the rock genre, but just where they fall in that genre and how much influence past groups have exerted on Tool is the subject of debate among both fans and casual listeners.

In many cases, Tool is categorized as alternative metal, a broad label used to loosely categorize bands (such as Jane's Addiction, Rage Against the Machine, and Faith No More, among others) that straddle the line between the aesthetics and fanbases of metal and alternative rock.

In a similar vein, Tool is categorized as a progressive rock (or “prog”) band. Those who feel that Tool are progressive rock artists frequently cite the popular (and admittedly broad) definition of prog. It is a style of rock music that seeks to move away from the mainstream by “pushing the envelope” of the rock genre, creating new sounds and styles that often possess a characteristically high level of layering and complexity, elements of which can easily be found in the band's music-for instance, the complex rhythms used in songs like “Schism” (5/8 to 7/8, or in 6.5/8 according to Justin Chancellor) and “Lateralus” (9/8 to 8/8 to 7/8), dissonance in other songs, the incorporation of a “pipe bomb microphone” (a guitar pickup mounted inside a brass cylinder), and a talk box guitar solo (“Jambi”), among many others.