Privacy

Last updated 23 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

Stacks is free, and affiliate commissions are part of how it pays for itself. When you buy something through a link on Stacks, the shop may pay us a small commission. It costs you nothing extra, and it has no effect on what gets recommended, how search ranks things, or any taste score. The things on a shelf are there because a person put them there.

Amazon Associates

As an Amazon Associate, Stacks earns from qualifying purchases. When somebody saves an Amazon link, we store it with our Associates tag on it, replacing anyone else's. If you follow one, Amazon sets its own cookies on amazon.com so it can credit the purchase to us, under Amazon's privacy notice. Amazon reports to us which products earned a commission and how much, never who bought them.

Impact

Our websites, onstacks.app and web.onstacks.app, load a script from Impact, an affiliate network that connects us with brands. It does two things. It turns links to brands we have a partnership with into tracked links, so a purchase after the click can be credited to us. And it records that a page was viewed. To do that it sets cookies in your browser and sends Impact the page's address, the page you came from, your IP address and basic details about your browser. The brand you visit learns that the visit came from Stacks. Impact handles that data under its own privacy policy. The Stacks iPhone app does not load that script.

Separately, a link to a brand we partner with through Impact, such as Target, passes through Impact on its way to the shop wherever you tap it, the app included. That short hop is how the shop knows to credit the purchase to us, and Impact sets its cookies in your browser as it happens.

Neither Amazon nor Impact receives your email address, your account, or what is on your shelves from us. If we add another affiliate network, it will be named here first.

Cookies

• Ours. Signing in on web.onstacks.app sets cookies that keep you signed in. They hold nothing but that, and signing out removes them.
• Impact's, on our websites, as described above. Blocking third party cookies or clearing them in your browser stops them, and nothing on Stacks breaks when you do.
• The shop's. Once you follow a link off Stacks, the site you land on sets whatever cookies it sets. That is between you and them.

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 to Amazon.
• Impact, for affiliate links to partner brands, on our websites.

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.