I review a lot of pull requests with Claude Code and Codex these days. The /review command is genuinely good — it reads the diff, spots the sharp edges, writes it up. But the output is always a wall of prose. On a PR that touches a request path across three services, I'd find myself drawing the call flow on a napkin to convince myself the review was right.
Meanwhile, the hosted reviewers — Greptile, CodeRabbit — just draw it for you. Every PR gets a tidy Mermaid sequence or flow diagram at the top of the review. It's lovely. I wanted that.
So I looked at what it would take.
What's notable here?
The hosted tools render those diagrams server-side: your diff goes to a third party, runs through their LLM, on their subscription. That's a lot of machinery for "turn this diff into a picture" — especially when my /review is already being written by a perfectly capable LLM running on my machine. The model that just understood the change well enough to critique it can obviously draw it.
