The Debugging Console mod greatly simplifies outputting of debug information to privileged users directly in-game, without the need for the ever so cumbersome minetest.chat_send_all().
Now it is as simple as calling printf(), which supports substitution of values a-la string.format() as well as lists of values if provided a table for its first argument. Helpful chat commands include /pipe for piping the input of any API function to the debug console for realtime inspection and /tail for continuously following the output stream of any plain-text log file on the server, such as debug.txt.
The console can also be toggled into a more compact form or hidden entirely by pressing SHIFT+E at any time. And with the /debug chat command, it's possible to copy the entire debug output into another application for more detailed review.