Rars: a Rust RAR implementation, mostly written by LLMs

#1

Post by davidsong » Wed, May 13, 2026, 7:59 PM UTC

I spent a fortnight using Claude to create specs for every version of RAR, then another using gpt-5.5 to write compressors in Rust.

It's not fast and it's not pretty, but it works.

Rars: a Rust RAR implementation, mostly written by LLMs
bitplane.net

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#2

Post by [deleted] » Wed, May 13, 2026, 7:59 PM UTC

[deleted]

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#3

Post by themafia » Wed, May 13, 2026, 8:19 PM UTC

> But, it works, and the world now has a free software RAR implementation.

Does it? How are you legally intending to use copyright to license this machine output? How would you know it's not encumbered in any way?

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#4

Post by cactusplant7374 » Wed, May 13, 2026, 8:21 PM UTC

> and it almost earned me an OpenAI ban

Were you flagged for a cybersecurity violation?

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#5

Post by esafak » Wed, May 13, 2026, 8:24 PM UTC

> It’s sloppy, it’s slow, it’s almost two megabytes in size and somewhat worse than WinRAR on compression.

As mathematicians say, optimization is left as an exercise to the reader. You did the hard part.

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#6

Post by gibspaulding » Wed, May 13, 2026, 8:33 PM UTC

cactusplant7374 wrote: post #4

> and it almost earned me an OpenAI ban Were you flagged for a cybersecurity violation?

> Well, it turned out that at some time during spec investigation, Claude needed to understand authenticity verification which is a paid feature. With a context full of reverse engineering tools it cracked WinRAR and bypassed product registration, then dutifully documented its crimes in the spec. The docs, when viewed, triggered OpenAI’s alarms and stopped it dead in its tracks. I squashed this out of the git history, and decided not to implement the feature at all.

You can draw your own conclusions as to what this says about the state of agentic development.

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#7

Post by Imustaskforhelp » Wed, May 13, 2026, 8:39 PM UTC

Kudos, this is a really cool project (even if it might be AI generated), I have starred the repo, (3rd starrer here)

One thing I have been curious at is are there any ways to stop a rar compression mid way and then continue it later?

Like suppose I have a compression happening for a large file, then would there be a possibility with this project to shut down the computer mid compression and continue it after starting it again?

I would really love it if you can add this functionality!

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#8

Post by slopinthebag » Wed, May 13, 2026, 8:39 PM UTC

How do we know it's actually correct?

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#9

Post by perching_aix » Wed, May 13, 2026, 8:43 PM UTC

slopinthebag wrote: post #8

How do we know it's actually correct?

By using it.

Re: Rars: a Rust RAR implementation, mostly written by LLMs

#10

Post by xphos » Wed, May 13, 2026, 8:45 PM UTC

Would it really take 5 years to develop rare compress and decompression that seems an extreme overestimate in time. I don't know of the compressor decompression but that seems really high