Notes:

• Also try BQNPAD, a third-party REPL with an interactive session format. And CBQN is the much faster offline interpreter (more options).
• The top bar has everything you need to know about BQN's special characters. Click to enter it, hover to see its name and the backslash combination you can type instead, and middle- or modified click to go to a help page.
• The code window is vertically resizeable.