Comment by flohofwoe

This is a point I see discussed surprisingly little. Given that many (most?) programmers like designing and writing code (excluding boilerplate), and not particularly enjoy reviewing code, it certainly feels backwards to make the AI write the code and relegate the programmer to reviewing it. (I know, of course, that the whole thing is being sold to stakeholders as "LoC machine goes brrrr" – code review? what's that?)

> When I ask Claude to find bugs in my 20kloc C library it more or less just splits the file(s) into smaller chunks and greps for specific code patterns and in the end just gives me a list of my own FIXME comments (lol), which tbh is quite underwhelming - a simple bash script could do that too.

Here's a technique that often works well for me: When you get unexpectedly poor results, ask the LLM what it thinks an effective prompt would look like, e.g. "How would you prompt Claude Code to create a plan to effectively review code for logic bugs, ignoring things like FIXME and TODO comments?"

The resulting prompt is too long to quote, but you can see the raw result here: https://gist.github.com/CharlesWiltgen/ef21b97fd4ffc2f08560f...

From there, you can make any needed improvements, turn it into an agent, etc.

My thoughts exactly. So many actually useful tools could be built on top of LLMs, but most of the resources go into the no code space.

I get it though, non programmers or weak programmers don't scrutinise the results and are more likely to be happy to pay. Still, bit of a shame.

Maybe these tools exist, but at least to me, they don't surface among all the noise.

Cursor BugBot is pretty good for this, we did the free trial and it was so popular with our devs that we ended up keeping it. Occasional false positives aside, it's very useful. It saves time for both the PR submitter and the reviewer.

I found GPT-5 to be very much less sycophantic than other models when it comes to this stuff, so your mention of 'everything looking great yay good job high-five' surprises me. Using it via Codex CLI it often questions things. Gemini 2.5 Pro is also good on this.

> When I ask Claude to find bugs in my 20kloc C library it more or less just splits the file(s) into smaller chunks and greps for specific code patterns and in the end just gives me a list of my own FIXME comments (lol), which tbh is quite underwhelming - a simple bash script could do that too.

I explicitly asked it to read all the code (within Cline) and it did so, gave me a dozen action items by the end of it, on a Django project. Most were a bit nitpicky, but two or three issues were more serious. I found it pretty useful!

I've had reasonably good success with asking Claude things like: "There's a bug somewhere that is causing slow response times on several endpoints, including <xyz>. Sometimes response times can get to several seconds long, and don't look correlated with CPU or memory usage. Database CPU and memory also don't seem to correlate. What is the issue?" I have to iterate a few times but it's hinted me a few really tricky issues that would have probably taken hours to find.

Definitely optimistic for this way to use AI

In an application I'm working on, I use gpt-oss-20B. In a prompt I dump in the OWASP Top 10 web vulnerabilities, and a note that it should only comment on "definitive vulnerabilities". Has been pretty effective in finding vulnerabilities in the code I write (and it's one of the poorest-rated models if you look at some comments).

Where I still need to extend this, is to introduce function calling in the flow, when "it has doubts" during reasoning, would be the right time to call out a tool that would expand the context its working with (pull in other files, etc).

I've "worked" with Claude Code to find a long standing set of complex bugs over the last couple of days, and it can do so much more. It's come up with hypotheses, tested them, used gdb in batch mode when the hypotheses failed in order to trace what happened at the assembly level, and compared with the asm dump of the code in question.

It still needs guidance, but it quashed bugs yesterday that I've previously spent many days on without finding a solution for.

It can be tricky, but they definitely can be significant aid for even very complex bugs.

I use Zed's "Ask" mode for this all the time. It's a read only mode where the LLM focuses on figuring out the codebase instead of modifying it. You can toggle it freely mid conversation.

Indeed, in many machine learning models, classification is always easier than generation. Maybe that's consistent with chatgpts intelligence level

i've had great success with both chatGPT and claude with the prompt "tell me how this sucks" or "why is this shit". being a bit more crass seems to bump it out of the sycophantic mode, and being more open-ended in the type of problems you want it to find seems to yield better results.

but i've been limiting it to a lot less than 20k LoC, i'm sticking with stuff i can just paste into the chat window.

Suggestion: run a regex to remove those FIXME comments first, then try the experiment again.

I often use Claude/GPT-5/etc to analyze existing repositories while deliberately omitting the tests and documentation folders because I don't want them to influence the answers I'm getting about the code - because if I'm asking a question it's likely the documentation has failed to answer it already!