Profiling zsh startup speeds

Profiling a slow zsh startup time can be done with the builtin module zprof.

Enabling zprof

Outside of Nix systems, you can enable zprof by adding the mod to the top and bottom of your ~/.zshrc:

zmodload zsh/zprof

# remainder of your .zshrc

zprof

Nix users can use the provided Home Manager option programs.zsh.zprof.enable:

{
    programs.zsh = {
        enable = true;

        # Enable profiling
        zprof.enable = true;
    };
}