Debugging does not always happen beside a laptop. This small OLED serial monitor puts the output of Serial.print directly on the breadboard, making it easier to see what a portable prototype is doing.

It needs power, ground and RX. Connect RX to the host's serial transmit output and send at 9600 baud; incoming text appears on the 0.96-inch OLED and scrolls as the display fills.

Backspace and clear-screen control characters provide a little control over the readout. The small screen encourages concise messages, but that can be enough to expose a state change or sensor value when a computer connection would be awkward.

Documentation: https://www.questwiseventures.com/products/mini-0-96-oled-breadboard-debugging-serial-monitor