Shepardson Microsystems used a cross-compiler to write BASIC, and at the same time they began development of their own assembler which was later released as the Atari Assembler Editor in ROM cartridge format. Assembler/Editor lacked many features, and was only suitable for small programs, so Atari also released the disk-based high-end Atari Macro Assembler. Macro Assembler was glacially slow, as it was entirely disk based. This led to a thriving market for 3rd party assemblers and debuggers to fix the problems seen in one or the other.
; Excel table with all opcodes and comparision between different Assemblers
; Mac/65 compatible cross assembler
; powerful and modern cross assembler under constant development
; xasm is a 6502 cross-assembler with some syntax extensions. By default it generates binaries for Atari 8-bit computers.
; smartest development environment available
; detailed and easy-to-read introduction to programming 6502-assembly on the Atari using Assembler/Editor.