Arduino Lab
Run real Arduino sketches on a simulated board, right here. Load one of my project boards or the starter kit, change the code, and press the parts. When you make something you like, copy the share link.
What it supports
setup() and loop(), variables and arrays, functions, if/for/while/switch, #define, and the core Arduino calls: pinMode, digitalWrite, digitalRead, analogRead, analogWrite, millis, delay, tone, map, random and Serial.print. Numbers use the same sizes as an Arduino Uno, so an int still overflows past 32,767.
What it doesn't
Libraries (#include), String objects, pointers, interrupts and timing tricks below a millisecond. It interprets your code rather than compiling it, so it's a place to learn and experiment, not a replacement for testing on real hardware.