How We Got an LLM to Draw Charts Without Ever Touching a Pixel

Let's get something out of the way first. Having data is good. Having a database full of reviews, commits, and org activity sitting there quietly, untouched, unread, never once glanced at by a human being with a coffee and an opinion? That's not "having data." That's a very expensive data graveyard. At LiveReview , we build what we call a Blast-Radius Aware AI Code Review for Business-Critical Systems . Which is a fancy way of saying: we review your code, we figure out how bad it would be if a change goes wrong, and we don't shut up about it until someone fixes it. Along the way we accumulate a review data: who reviewed, how much, how fast, how often, which repos are on fire. And for a while, that pile just sat there. Engineering leaders would ask "is adoption increasing?" and get back a vibe, not an answer. So we built Livi , a chat bot that answers real questions about that data with real charts, not paragraphs of hedging. This post technically about how Livi draws those charts. Specifically: why we never let the LLM touch a pixel, how the same chart definition ends up as both a live interactive graph in your browser and a flat PNG in a Slack thread, and why teaching a language model to pick the right chart shape is a surprisingly deep rabbit hole. The core decision: don't ask the LLM to draw, ask it to describe The tempting, wrong idea is: "let's have the LLM generate an image." Please don't. Image-generating models are a different beast entirely, and even if you got one to draw a bar chart, you'd have no way to verify the numbers on it are real. You'd be trusting a model that hallucinates plausible-sounding review counts to also render them faithfully into pixels. That's not a chart, that's chart-shaped fan fiction. The actually good idea, and the one every serious LLM-charting integration eventually converges on, is: the LLM writes Vega-Lite , a JSON grammar for describing charts declaratively. You don't say "draw a blue bar going up." You say: { "mark" : "bar"