Your mail stays on your machine. The thinking runs on the Claude subscription you already pay for.
Version 1.1.0 · Universal — one file, Apple Silicon and Intel · 208 MB
Letterknife doesn't sell you tokens — it drives Claude Code on your own subscription. Install it, run claude login, and Letterknife will walk you through the rest on first launch.
The app isn't signed with an Apple certificate yet, so the first time you open it macOS says it can't check it for malicious software. It's a scary message about an unsigned app, not a broken one. Open it once via System Settings → Privacy & Security → scroll down → Open Anyway. After that it launches normally, forever.
On older macOS (before Sequoia) right-clicking the app and choosing Open does the same job.
Prefer the source? Read the docs.