Privacy

What Lemma collects, and why

Last updated: October 2026.

What	When	Why	Kept
An anonymous id in a cookie (lemma_anon)	Every visitor	To count which problems are viewed and answered, without knowing who you are	400 days in your browser
Answers you enter and problems you view	When you use a problem	Your progress, streak and review, and overall statistics on how hard problems are	Until you ask us to delete them
Your name and email	If you sign in	Held by Clerk, our sign-in provider, to run your account	Until you delete your account
Work you submit to “Check your work”, and what Lemma read from it	When you check work	To grade it and show your history. Photos are read and not stored; the text read from them is.	Until you ask us to delete it
A check you make before signing in	Your first check of the day without an account	To show you the result. It moves to your account if you sign in. To limit these checks we keep a one-way scramble of your network address for that day, never the address itself.	30 days if you don’t sign in
Solutions, problems and comments you post	When you post them	To show them on the site	Until you delete them or ask us to
Your subscription status	If you subscribe to Lemma Plus	To give you Plus. Card details go to Stripe and never reach Lemma.	While you subscribe, and as tax law requires

Who processes it

Vercel: hosting.
Neon: our database.
Clerk: accounts and sign-in (and Google, if you choose to sign in with Google).
Groq: the AI that reads and grades work you submit. It receives that work's text or images for the request.
Stripe: payments, only if you subscribe to Lemma Plus.

What we don't do

No advertising, no selling or renting your data, and no tracking you across other sites.

Your choices

Ask for a copy of your data, or for it to be deleted, at support@lemmaproof.com. We handle requests by hand within 30 days. Deleting your account removes your sign-in; write to us as well to have your work and history removed.

Children

Lemma is for people aged 13 and over. If you believe a child under 13 has an account, write to support@lemmaproof.com and we will delete it.

For parents and guardians

Lemma is a maths practice site for people 13and over. Learners solve problems and can have their written working checked by an AI, which points to the first step that doesn't hold rather than giving the answer. There are no ads and no private chat. Learners can post solutions and comments, which others can see; a share link is made only if your child chooses to make one. To see or delete your child's data, write to support@lemmaproof.com.