Privacy

Last updated 21 September 2026. Stacks is made by The Red Collar Company.

The short version. Stacks holds what you put on your shelves and the email address you signed in with. It is not sold, and there are no ads to target with it. What follows is the long version, including the parts that are less obvious, like the fact that the name of a thing you save is read by a machine somewhere else in order to work out what it is.

What is collected

Your account

Signing in with Google or Apple gives us your email address and display name. Signing in with an email and password stores that address and a hashed password, never the password itself.

What you put on a shelf

Shelves, the things on them, your notes, the links you paste and the pictures you upload. A shelf you make public is visible to anybody, including on a share link that needs no account to open. A private shelf is visible only to you.

Device tokens

If you turn on notifications, a token for your device is stored so we can send them. Turning notifications off removes it.

Ordinary server logs

Requests to the service are logged with an IP address and a timestamp, as any server does, to keep the thing running and to stop abuse.

What is done with it

• Showing your shelves to you, and your public shelves to whoever opens them.
• Working out what a thing is, so it can be found by more than its exact name.
• Comparing your taste with other people's.
• Sending the notifications you asked for.
• Finding a picture and somewhere to buy an item you saved.

Machines that read what you save

This is the part most policies leave out, so it gets its own section. To work out what a thing is, what it is like, and what you meant by a search, Stacks sends text to two outside services:

• Google (Gemini) and TypeSafe receive the name of an item, the name of the shelf it was saved to, and the words you type into search. They do not receive your email address, your account identifier, or any way of telling one person from another.
• When you save a link, our server fetches that page to find a picture and a description, the same way a link preview works anywhere else. It may also look a thing up on Wikipedia or search for somewhere to buy it through Brave Search.

None of this is used to build an advertising profile, because there is no advertising.

Taste matching

Your shelves are reduced to a set of weighted traits, and two people are compared on those traits, on how much of each other's range they cover, and on the things they genuinely both hold. It runs on our server. A score is visible to you and to the person you matched with, and to nobody else. Only public shelves are ever compared.

Affiliate links

Some product links carry an affiliate tag, and a purchase may earn us a commission at no extra cost to you. Following one tells the shop that the visit came from us. It does not tell them who you are, and it has no effect on what gets recommended or on any taste score.

Where it lives, and who else touches it

Data sits in a PostgreSQL database hosted on Railway, with uploaded pictures in an S3 compatible object store. Everything travels over HTTPS. It is not sold to anybody.

• Railway, hosting for the service, the database and the cache.
• Google Sign-In and Apple Sign-In, for signing in.
• Firebase Cloud Messaging, to deliver notifications.
• Google (Gemini) and TypeSafe, as described above.
• Brave Search, to find where a thing can be bought.
• Amazon Associates, for affiliate links.

Children

Stacks is not meant for children under 13, and we do not knowingly collect anything from them.

Keeping and deleting

Your data is kept while your account exists. You can delete the account from inside the app, which removes your shelves, your items, your notes and your account record. Deletion is processed within 30 days. Copies may sit in encrypted backups for a short period after that before they age out.

What you can ask for

• A copy of what we hold about you.
• A correction to anything wrong.
• Deletion of your account and its contents.
• An export of your shelves.
• Control of notifications, from the app's settings.

Changes

This page will change as the app does. Anything significant will be said in the app rather than quietly edited here.

Asking about any of this

Write to stacks@redcollar.io.