The 29th International Obfuscated C Code Contest (IOCCC) 2025 Winners

The GameBoy emulator's code also looks like the GameBoy. Slow clap this is insane, definitely my favorite entry.

https://github.com/ioccc-src/winner/blob/master/2025/ncw1/pr...

The author, Nick Craig-Wood, is the creator of rclone!

My favorite is the 366-byte C program emulator that can run Linux and Doom [0]. The VM implements an OISC - a One Instruction Set Computer [1].

[0] https://github.com/ioccc-src/winner/blob/master/2025/cable/p...

[1] https://github.com/ioccc-src/winner/blob/master/2025/cable/R...

In case anyone was wondering, the IOCCC specifically permits LLM use in their guidelines.

"The IOCCC has a rich history of remarkable winning entries created by authors who skillfully employed various techniques (often their own tools) to develop their code."

The website itself is obfuscated, it’s not easy to find the C sources at all!

There's a Frieren [1] reference in there! https://www.ioccc.org/2025/yang2/index.html

One of the main characters is called Fern, and she almost exclusively uses the common offensive magic of Zoltraak.

[1] https://en.wikipedia.org/wiki/Frieren

I with the Underhanded C Contest would come back, it was far more interesting to me. No disrespect intended to the Obfuscated C competitors.

OMG, my game boy game of life implementation is included in one of the winning entries!

Back in 2000 I was being interviewed for my first internship, to join a team of C programmers. They showed me one of the winner entries of the prior years, asked me to review the code and left the room. About 5 minutes later they came back:

– And?

– I'm sorry I wasted your time. I just can't understand it.

They burst into laughs and asked me to start the joining process.

I wonder if people still make fun of interns. I still have a good laugh when I remember myself freaking out.

I love the submissions of IOCCC generally, but the schedule and submission process looks like a mess, is that part of the joke? Or is it just because being consistent and designing a simple process is hard¡

There's another contest called Underhanded C that I enjoyed a lot reading, but it has been inactive for a decade at this point...

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I'm not sure this kind of competition is still meaningful, given that LLM can easily convert a program clearly written in any programming language to the most obfuscated C code, and can still easily verify it's correctness in an automated way.

Do I miss anything?

Tis a pity to not have LLMs compete, given level of obfuscation they be capable of.

So like at a film festival, 90% of the entries won a price, but unlike a film festival there's not a single best. Weird, like modern education.