A working bass line has two jobs: state the harmony, and lead the ear to what's next. That means a chord tone on beat 1 of every bar — the downbeat has to be legible even with no piano in the room — and, on the last beat before a new chord, an approach tone (a half or whole step, or a chord tone of what's coming) that pulls straight into the next root. Everything between is free. Generate a line, then move any note with the arrows and watch it get graded live.