Your AI-tool usage is invisible. Here are 4 tiny local tools to see it.

You use Claude Code, or ChatGPT, or both, every day. Quick question: how many messages did you send last month? Which model ate most of your budget? How much did prompt caching actually save you? You don't know. I didn't either. That's a weird gap. We instrument everything else — git activity, deploy frequency, test coverage — but the tool we now spend the most hours inside is a black box. The vendor dashboard, if it exists, is a billing page, not a mirror. So I built four tiny tools to fix that for myself. They all run 100% locally . No accounts, no API keys, no telemetry, no network calls. They read files that are already on your disk and print something you can look at. All four are open source on github.com/greymoth-jp — and because that's a real claim, the only thing I'll ask is that you grep the source yourself before you trust me. Here's the privacy point up front, because it's the whole design: these read your data, but your data never leaves your machine. That's not a feature I'm bolting on for a marketing line. It's the reason the tools are small enough to audit in one sitting. The one number that changed how I work Before the tools, here's what I assumed: my Claude Code bill is dominated by the prompts I write, so to spend less I should write tighter prompts. Compress the context. Trim the system message. The usual advice. I ran the numbers on my own ~/.claude transcripts and got this: component share of cost cacheRead 72% cacheWrite ~19% output the rest input ~0.3% Input — the thing everyone tells you to compress — was 0.3% of my spend. Compressing my prompts to save money would've been optimizing the rounding error. Worse: compressing a static prompt changes its bytes, which busts the prefix cache, which can make the bill go up . The real cost center was cache reads: long sessions dragging a fat context forward, turn after turn. That points at completely different levers — cache hygiene (milestone /compact , /clear before the context balloons, keeping C