I've been building A9 Tracker because I needed it myself. The LEAP and EAT studies changed the pediatric advice on food allergens from "wait as long as possible" to "introduce early, then keep it up" — the Big 9 (peanut, egg, milk, tree nuts, wheat, soy, fish, shellfish, sesame), each fed a couple of times a week, for months. That's a great protocol and a terrible thing to hold in your head. By week three I couldn't reliably tell you whether we'd hit peanut twice that week or once, and my wife and I were duplicating and dropping servings because neither of us knew what the other had already logged.

The non-obvious call wasn't a feature — it was two things I kept refusing to build. First: A9 Tracker never gets to have a medical opinion. Every clinical claim in the app is attributed to "pediatric guidance" or "the LEAP/EAT studies," never stated as the app's own instruction — it's a tracker, not a recommendation engine, and that's a line I've had to re-draw more than once when a later change let a sentence drift back into the app's voice. Second, and the one I had to keep talking myself out of expanding: no recipe ideas, no prep tips, no symptom journal, none of the stuff other allergen apps pile on. This isn't a thing you use for a week and delete — the protocol runs until a kid's about five, so it's a five-year-old app on day one. Every extra tap or screen you add is a cost you pay a few times a week for four and a half years, and the feature that saves someone thirty seconds of scrolling once will cost everyone thirty seconds of friction every week after that.

What's left is deliberately small: pick an allergen to introduce, tap Serve when you feed it, see the week's progress at a glance, sync with whoever else feeds your kid. That's it. Introducing a new allergen is a plain list of the Big 9 plus whatever custom foods you add — no explainer, no upsell, no "here's a recipe" screen in the way of the one thing you opened the app to do.

It's live at a9-tracker.web.app — free, no account required to start logging. If you're in the middle of allergen introduction with a baby or toddler, give it a try; and always follow your pediatrician's actual guidance over anything an app tells you.