Less ambitiously, how small and clear could you make a program for QED calculations? Where you're going for code that can be clear to someone educated with only

Less ambitiously, how small and clear could you make a program for QED calculations? Where you're going for code that can be clear to someone educated with only undergrad physics, with effort, to help explain what the theory even is -- not for usefulness to career physicists. Maybe still too ambitious, because I haven't heard of such a program.