Last updated November 13, 2026.
Stack is software for tracking training, food and health, used by individuals and by coaches working with their clients. It is made and run by Dad with Style OÜ, Sepapaja tn 6, Tallinn 15551, Estonia (registry code 14696867). Write to [email protected] about anything in this policy. We answer within one month.
This policy covers subscribers, who sign up in the iPhone app and have no coach; clients of a coach, who use Stack because their coach invited them; coaches; and visitors to getstack.to.
We also coach clients ourselves, as Founder Athlete OS. For its clients we are the controller of everything, and its privacy notice applies as well as this policy.
Your email address and your consent to the handling of your health data are required to use Stack, because tracking that data is what Stack does. If you decline, you can delete your account. Everything else is optional; a feature you skip works without its data.
Where your coach is the controller, your coach decides the purpose and the legal basis for your coaching records. Otherwise:
We never sell your data, never show you ads or use your data for ads by others, and never track you across other apps or websites. Apple Health data is never used for marketing. A coach may publish a result only with your written permission.
AI food reads, with the yes you give when you sign up: when you log food from a photo or a sentence, it goes to Anthropic, whose AI model reads it, with a list of what you logged in the last 7 days (food names, amounts, day and meal). A photo is not stored. Anthropic handles this under a data processing agreement, does not train its models on it, and normally deletes it within 30 days; its safety systems can keep flagged content longer. The result is marked as an AI estimate. You can switch AI reads off in Settings, then Privacy, and log food by hand.
Problem reports, said on the report sheet above Send: when you send one, what you wrote and any screenshot go to Anthropic under the same agreement, and its model writes a one-line description of the problem, told to leave out your name and anything else about you. Our automated checks use that line to find and fix the fault. Anthropic does not train on your report and normally deletes it within 30 days; we keep your words and screenshot to answer you, and your coach can see them if you have one. If you switched AI reads off in Settings, then Privacy, your report is not read this way; our staff read it instead.
Calories and nutrients come from FoodData Central (US Department of Agriculture), asked by our server, and Open Food Facts, asked by your phone when you scan a barcode, so it sees your phone’s internet address. Neither receives your name or your diary.
Stack keeps the words you searched or said with the entry you kept, and your corrections to foods and menu dishes it read, with names and health details removed and no link to your account.
When you speak a meal, your iPhone turns the speech into text, on the phone whenever it can; in Chrome and browsers built on it, the browser’s maker does. Stack receives only the text.
Your own AI. You can connect an AI you already use, such as Claude or ChatGPT, in Settings. It can read your profile, weight and measurements, workouts and program, food diary and targets, active days, sleep and this week’s step from your Brief. It never sees your photos. From Apple Health it sees only your steps and your morning weight, and only while Apple Health in your AI is on in Settings, then Privacy. Making a new link in Connect your AI, which names them, turns it on. It can’t change anything, except that a subscriber’s AI can save a program as a draft, which changes nothing until you tap Use it. What it reads is handled by the company that runs it, under its own terms. To stop it, remove Stack from your AI’s connectors; a new link from Settings also ends the old one. We record when your AI asked and which kind of question, never the question or the answer.
Call notes, if you have a coach, with the yes you give when you sign up: Stack reads your coaching call transcripts and sends them to Anthropic under the same agreement, and its model keeps only the coaching: training, food, targets, decisions and next steps. You, your coach and your connected AI can read the notes. They can include your daily steps from Apple Health. You or your coach can switch them off; deleting your account ends them too. How calls are recorded is your coach’s decision and is set out in your coach’s privacy notice.
Stack chooses prewritten sentences and suggestions from your own entries, such as the line under a chart. None of them has a legal or similarly significant effect on you, a change to your targets happens only when you or your coach makes it, and your health answers never change your targets on their own.
To find faults before they reach you, automated checks, including an AI assistant (Claude, by Anthropic), test the app every week and when something looks wrong. They work on test accounts we create for the purpose. Code running on GitHub also checks coached clients’ Progress summaries and passes on only counts. From real use, the checks get nothing about who: counts, such as how many buttons didn’t respond and how many saves didn’t arrive; each problem report as that one-line description; and, with no account attached, the words of a food search that failed and the number of a barcode the scanner couldn’t read.
Our list of service providers names each company, what it does and where. Each works under a contract requiring it to protect your data as this policy describes. Apple Health, speech recognition, the YouTube player, Open Food Facts and an AI you connect yourself act for themselves under their own terms.
Some of these companies are based in the United States, so your data can be reached from there. Those transfers rest on the European Commission’s standard contractual clauses or the EU–US Data Privacy Framework; we send a copy of the clauses on request. If you live outside the EU, your data is stored and handled outside your country, where courts and authorities can reach it under local law.
Analytics, only if you allow it in the app: we count what happens with PostHog (EU), such as that a weigh-in was logged, which screen opened and which buttons were tapped (never their text), with your account ID and first name. No weight, measurement, food, note or photo is sent, and your screen is never recorded. Without your yes, we count only from what our own server already records, with nothing sent from your device. Crash and error reports the app needs in order to work are sent without your figures. You can change your answer in Settings.
Notifications are off until you turn them on and never contain a weight, a food or a health detail. In the web app, they travel through Apple’s or Google’s push service, encrypted so only your device can read them.
Stack keeps your sign-in and a copy of your own data on your phone so it opens fast and works offline. Signing out removes them once unsaved changes are sent. There are no advertising cookies, and Stack works the same whether or not your browser sends a Do Not Track signal.
When you visit getstack.to, we count the visit with PostHog (EU) to learn which links bring people to Stack: the page you opened, the site or link that sent you, how far you scrolled, which buttons you tapped (never their text), and your browser, device, screen size and language. PostHog also keeps your internet address and the city and country it works out from it. Nothing is stored on your device, there is no cookie, your screen is never recorded, and a visit is not linked to an account. The App Store button tells Apple which link sent you. This is our legitimate interest; you can object by writing to us.
These rights are the same wherever you live. If you are a client of a coach, send requests about your coaching records to your coach; if you write to us, we pass them on and help your coach answer. Our consumer health data privacy policy covers health data separately, as Washington State’s law requires.
Data travels encrypted. The database itself refuses access to anyone who isn’t entitled to a record, photos are kept in private storage, and access to the systems is limited to the people who need it. If a breach puts your rights at risk, we tell you and the regulator as the law requires.
Stack is for adults. You can’t make an account if you are under 18. We don’t knowingly hold data about anyone under 18. If we learn that a user is under 18, we close the account and delete the data.
When this policy changes, the date at the top changes. If a change affects what we collect or who receives it, we tell you in the app or by email before it applies.
Terms · Service providers · Coach terms · Data processing agreement