Privacy Policy

Last updated October 12, 2026

The short version: we collect what you give us to coach you, we don't sell it, we don't show ads, and we don't track you across other apps or websites.

Stack Days is a website (stackdays.org) and an iPhone app, run by Will Loughlin. This policy covers both.

What we collect

• Account details: your name, email address and password (stored scrambled, we can't read it).
• Your training profile: what you tell the coach about where you're at and what you're going for, your experience level, sports, schedule, equipment and injuries, and, only if you add them, your birth year, sex, height and weight.
• Your training: the plans, sessions, goals and logs in your account (sets, reps, weights, effort, notes, heart rate during a session), and your conversations with the coach.
• Apple Health, only if you connect it in the iPhone app: your workouts from the last two years (type, start time, duration, distance, energy, average and maximum heart rate) and daily totals (steps, walking and running distance, active energy, exercise minutes, resting heart rate, VO2 max). While a session is open in the player, the app reads your live heart rate from Apple Health to show it to you, and saves the session's average and maximum with your log. When you finish a session, the app saves it to Apple Health as a workout.
• Strava, only if you connect it: your Strava activities (type, name, time, duration, distance, energy, heart rate) and the login token Strava gives us.
• Technical logs: our servers keep short-lived logs (IP address, requests, errors) to keep things running and stop abuse.

We use all of this for one thing: running Stack Days for you, which means building and adjusting your plan, coaching you, and showing your progress. Nothing is used for advertising or sold, and Apple Health data is never used for anything but your own training.

Who else sees it

• Anthropic (Claude): the coach is Claude, an AI model made by Anthropic. Each time the coach writes your plan or answers you, it's sent your training profile, your plan, recent and upcoming sessions and logs, your goals, recent workouts imported from Apple Health or Strava, the coach's notes about you, and the conversation. You agree to this before you start, and the coach doesn't run until you do. Anthropic processes it under its commercial terms to produce the reply, and doesn't use it to train its models. Daily step and heart rate totals aren't sent.
• Web search: the coach can search the web for drills and programs. Searches go through Anthropic and contain search terms, not your personal details.
• YouTube: when you watch a demo video, it plays from YouTube (youtube-nocookie.com on the website), and YouTube sees that request like any video you watch.
• Amazon Web Services (SES): sends our emails (your verification code and password resets), so it sees your email address.
• Cloudflare: sits in front of the website to protect it and speed it up.
• Strava: if you connect it, Strava knows Stack Days has access to your account until you disconnect.

Everything else is stored on our own servers in the United States. We'll only share information beyond this if the law requires it.

How long we keep it

As long as your account exists. The Stack tab only counts the last two years, and the app only sends that much from Apple Health. Disconnecting Strava deletes everything imported from it. Deleting your account (Settings, then Delete account, in the app or on the website) erases your profile, plans, sessions, goals, coach conversations and imported workouts straight away, and disconnects Strava. Backups roll over within 90 days. Workouts the app saved to Apple Health stay in Apple Health, where you control them.

Your choices

• Edit your training profile, or tell the coach to change its notes about you, at any time.
• Turn Apple Health access on or off in the Health app: tap your picture, then Apps, then Stack Days.
• Connect or disconnect Strava in Settings.
• Ask us for a copy of your data, or to correct or delete it, by emailing [email protected].

Security

Connections are encrypted, passwords are hashed with scrypt, and the iPhone app keeps its sign-in token in the iOS Keychain.

Kids

Stack Days isn't for anyone under 13, and we don't knowingly collect their information. If you think a child has an account, tell us and we'll delete it.

Changes and contact

If we change this policy in a meaningful way we'll tell you in the app. Questions: [email protected].