One of the most exciting challenges available to any software developer is that of writing brilliantly working code that’s so obtuse, so indecipherable, and opaque, that even its own author would struggle to grasp its inner workings after returning to it a year later. While for some this is just how they naturally write code, for others it’s part of the International Obfuscated C Coding Challenge (IOCCC), with 2025’s entrants once again showing their mettle.

The IOCCC judges entries among a range of categories, as it can be hard to otherwise quantify what is the ‘best’ entry, with ground rules limiting what the entry can entail. Generally as long as your code adheres to the C11 standard with a source size of 4,993 bytes or less and final binary size of under 2,503, is accompanied by a GNU-style Makefile and doesn’t turn a judge’s computer into a raging inferno — it should qualify.

Among the winning entries we got fun ones like ‘Most likely to shock’ by [Yusuke Endoh] which generates a Lichtenberg figure in ASCII in the terminal. There are also quite practical ones, such as the ‘Best real emulator’ winner by [Nick Craig-Wood], whose entry is a functional Game Boy emulator. Although not full-featured, it can play a range of real GB ROMs, just do not expect to get any sounds or fancy terminal-based graphics.