Lab
Things you can poke at
Serial is easier to believe once you can change a number and watch the result. Each of these runs entirely in your browser — nothing to install, no board needed.
What 8N1 actually means
Take a UART frame apart. Change the data bits, parity and stop bits and watch the waveform change with them.
Baud mismatch playground
Set two rates, type any text, and watch exactly which bytes arrive, which are rejected, and why the garbage looks the way it does.
How close is close enough?
Drag the clock error and watch where the receiver starts sampling the wrong bit — always at the stop bit, never at the start.
Which baud rate do I need?
Four questions that tell you whether the baud rate is your problem at all, and which number both ends should be set to.
Factory baud rates by module
What each module ships at — and the separate AT-mode rate that catches most people out.
These accompany the written fix for garbage in the Serial Monitor. Start there if you are stuck right now; come back here for why it works.