Breathe CLI – Paced resonance breathing in the macOS terminal

Marek Kowalczyk has heart failure—HFrEF, to be exact—so he built the one tool he couldn't find anywhere else. Breathe CLI is a terminal app that paces your breathing at exactly 6 breaths per minute, which sounds simple until you realize it's calibrated to resonance frequency, the specific breathing rate proven in peer-reviewed cardiology literature (Bernardi et al., Circulation 2002) to actually improve cardiac vagal tone and baroreflex sensitivity in heart patients. This isn't some wellness-app glow nonsense. It's a single Python file, stdlib only, zero dependencies, MIT licensed—just open terminal and follow the bar.

Here's what makes this different from every other "breathwork" app on the App Store: it's designed by someone who actually has skin in the game, and it's constrained by actual clinical evidence. No breath retention (Valsalva risk for cardiac patients). No rapid breathing (minimum 8-second cycles enforced). Exhale capped at 2x inhale because there's zero evidence extreme ratios do anything useful. And the best part—no account, no subscription, no app store waiting room. q or Ctrl+C exits immediately and restores your terminal even on crash. That level of respect for the user's time and autonomy is frankly rare.

He also included a resonance frequency measurement protocol in the README for anyone with a chest-strap HRV monitor who wants to find their personal optimum instead of the default 6 bpm. Because medicine isn't one-size-fits-all and Marek apparently actually gets that. Install via pip or Homebrew, all open source, zero friction. macOS only uses afplay for audio cues.