Awk! Awk! Add a diagram!: Greptile-style PR diagrams, minus the SaaS

Anton Yakutovich Posted on May 31 Awk! Awk! Add a diagram!: Greptile-style PR diagrams, minus the SaaS # github # codereview # agentskills 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. The diagram doesn't need a SaaS. It needs about thirty lines of glue. The idea: let the agent draw, let gh post That's the whole design of Iago 🦜 — a skill, not a service: The host agent draws the diagram. Iago's SKILL.md tells your agent which diagram type fits the diff and how to write valid Mermaid. No provider SDK, no API key — it uses the LLM you're already paying for. A tiny helper posts it. A single TypeScript file ( post.ts , run by bun ) finds your /review comment and appends the diagram via authenticated gh . That's the entire runtime: bun + gh . It's idempotent. Re-run it and it replaces its own block instead of stacking duplicates, using a pair of HTML markers. No server. No key. No diff leaves your machine except through the same gh you already trust. What it actually posts Iago auto-detects the diagram type from the diff — and you can always