Privacy policy
The short version: Stackt only keeps what it needs to deliver your Substacks to your Kobo. We do not sell your data, we do not run adverts, and we do not send marketing emails.
Who we are
Stackt is a small independent service run by an individual based in the United Kingdom. For questions about your data, email hello@kostackt.com.
What we collect, and why
- Your email address. Used to sign you in with a one-time link, and to identify your account. Legal basis: it is needed to provide the service you asked for.
- The Substack addresses you add. Used to check those publications for new posts.
- Your Dropbox connection. When you connect Dropbox we store a token that lets Stackt save files into the folder you choose. We never see your Dropbox password and we only write the EPUB files we create.
- Your chosen folder. The Dropbox folder your EPUBs are saved into.
- Your plan. Whether you have unlocked the paid plan, and the customer reference Stripe gives us. We never see or store your card details.
- Your Daily Stacks choices. Which optional daily extras you have switched on, and your sudoku difficulty, so we can send you the right ones.
The EPUB files
We fetch the public posts from the Substacks you add, convert them to EPUB and save them into your Dropbox. We do not keep a copy of the posts or the EPUB files ourselves. The optional daily extras are made from public sources, and nothing about you is sent to them.
Who handles your data
We use a small number of services to run Stackt. They process your data only to provide their part of the service:
- Vercel, which hosts the website and runs the daily job.
- Supabase, which stores accounts, your Substack list and sign-in.
- Dropbox, where your EPUB files are saved.
- Stripe, which takes payment for the paid plan.
- ImprovMX, which forwards emails sent to our contact address to us.
Some of these providers process data outside the UK. Where they do, they rely on recognised safeguards for international transfers.
Cookies
We use only the cookie needed to keep you signed in. We do not use advertising or tracking cookies.
How long we keep it
We keep your data for as long as you have an account. If you ask us to delete your account, we delete your email, Substack list, Dropbox connection and plan details. Records of a payment may be kept by Stripe for as long as the law requires them to.
Your rights
Under UK data protection law you can ask to see the data we hold about you, correct it, or have it deleted. You can also disconnect Dropbox at any time from your dashboard, which removes our access straight away. To make a request, email hello@kostackt.com from the address you signed up with. If you are unhappy with how we have handled your data, you can complain to the Information Commissioner's Office at ico.org.uk.
Changes
If we change how we use your data, for example by adding emails about new features, we will update this page first and ask for your consent before sending you anything. Last updated 20 October 2026.