Boolean — c.Bool()

One byte: 0 is false, any non-zero byte reads as true; writes 0 or 1 (matches blf_lib Bool):

@c.struct()
class AuthorFlags {
  @c.field(c.Bool())
  is_online!: boolean;
}

C equivalent:

typedef struct {
    uint8_t is_online; /* 0 = false, non-zero = true */
} AuthorFlags;

(bool is_online is also one byte on most ABIs, but game formats usually use an explicit integer type.)

For combinable flag bits in one integer, use Bitfield instead.