The rtlpp.toml manifest

The rtlpp.toml file that names a project's top module, board, device, constraint file and build settings, and where to change each one.

The manifest is the project's settings as a small TOML file. It is written beside the files when you export, read back when you import, and shown live in the Inspector under rtlpp.toml.

The manifest of a project for the iCEBreaker:

name = "Blink"
top = "blink"
board = "icebreaker"
constraints = "icebreaker.pcf"

[device]
family = "ice40"
part = "up5k"
package = "sg48"

[build]
seed = 1

name: The project name.
top: The module synthesized for the device. Without one, RTL++ picks the first design module that no other module instantiates.
board: The board, which also sets the device. Omitted for a simulation-only project.
constraints: The pin constraint file in the project: .pcf for iCE40, .lpf for ECP5, .cst for Gowin.
[device]: The FPGA as nextpnr names it: family, part and package. Omitted for a simulation-only project.
[build]: The placement seed and, when set, the target clock frequency freq_mhz. See Seeds and target frequency.

Change the top module, board, device and constraints in the Inspector (⌘E), and the seed and target frequency in the Build view. The command bar also offers to set the top module when it finds a likelier one.