A machine code monitor (aka machine language monitor) is software built-into or separately available for various computers, allowing the user to enter commands to view and change the memory of the machine, with options to load and save memory contents from/to secondary storage.

Machine code monitors became something of a mass software product in the home computer era of the late 1970s and into the 1980s. Some full-featured machine code monitors provided detailed control of the execution of machine language programs (much like a debugger), and included absolute-address assembler and disassembler capability. It was not unheard of to do all of one's programming with a monitor (indeed, in the first years of home computing, many people made do with POKE'ing hand-assembled opcodes and operands into program memory).