Definition
A tool can be a separate hotend, an extruder feeding a shared nozzle, a mixing channel, an MMU input or another machine-defined resource. The T number selects a slot, while firmware or macros may park, unload, heat, wipe, apply offsets and prime around the change.
Slicers also add purge towers, wipe paths or ramming moves so the next deposited material is stable. Those explicit moves are visible in the file; hidden macro motion is not. Tool number, filament name and color are independent unless trustworthy metadata or user input connects them.
What matters in practice
Slot is not material
T1 identifies a configured slot, not a guaranteed polymer, color, diameter or nozzle.
Changes have hidden state
Offsets, heaters, per-tool E positions and macros can all change when a tool becomes active.
Purging is separate geometry
A purge tower or wipe path is generated motion, not an automatic property of the T line.
Example in G-code
Two explicit tool slots
T0
G1 X40 Y20 E1.2
T1
G1 X60 Y20 E1.2The two T lines select slots 0 and 1. The file does not state which materials are physically loaded, and no hidden parking motion is shown.
What this viewer can show
The viewer tracks supported tool slots and their extrusion separately and can color the toolpath by active tool. It does not infer material identity, model hidden macros or guarantee that the target machine has those tools installed.
Primary sources
This explanation uses firmware documentation and details visible in G-code. Your printer's settings still determine what the machine does.