The Atari BASIC language was released in 1979 along with the Atari 400 and 800 computers. Atari BASIC came in a plug-in cartridge: it wasn’t built into the computer, which was unusual for microcomputers at the time.
The first version of BASIC (Beginners’ All-purpose Symbolic Instruction Code) was released in 1964. Atari’s version (not coded by Microsoft, another oddity for the era) added commands for harnessing its computers’ graphics, sound, and other special features.
BASIC is the default language for Atari 8-Bit Bot. Just start your code after @Atari8BitBot — you don’t need to put a directive in brackets. Don’t forget to hit RETURN before each new line of code.
This is important: if the BASIC parser can’t understand something about your program (for instance, if you tell it PRIMT instead of PRINT) it simply won’t respond. On a real Atari, BASIC would tell you right away if something was amiss. On Twitter, it really isn’t feasible. So if you don’t get a reply within two or three minutes, check your code a try again. Or ask for help — it is Twitter, after all.
Internet Archive has scans of many books about Atari BASIC, helpful whether you’re starting from nothing or just haven’t used it in a few decades. If you’re new to BASIC, try this book. Atari’s own BASIC Reference Manual is great if you know the basics but need some reminders.
When you’re ready for some extra fun with BASIC: the bot also understands Turbo-BASIC XL.