Terms of Service

1. Who you are contracting with

These terms are the agreement between you and 2Sigma for your use of the 2Sigma service at 2sigma.app. By creating an account, or by subscribing to a paid plan, you accept them.

2Sigma is run from the United States by a sole proprietor, not by an incorporated company, so there is no company registration number to give.

Questions and notices, including a cancellation under section 6, reach us at [email protected]. We answer there rather than by telephone.

2. What the service is

2Sigma serves you past-exam questions from your course, adapts what it serves to how you are doing, and gives you an AI tutor ("Sigmund") that talks you through a question and grades your answer.

Sigmund is an AI, not a person, and it can be wrong. Scores, feedback, explanations and study recommendations are study aids. They are not a guarantee that an answer is correct, not a prediction of your grade, and not a substitute for your course's own material or your instructor.

3. Who may use it

You must be 18 or older to use 2Sigma. By signing in you confirm that you are. The account is yours personally; do not share your login, and tell us promptly if you think someone else has used it.

4. Plans and monthly allowances

2Sigma is sold as a subscription. Every account is on a plan — Free, Student or Pro — and every plan carries two allowances for the month:

• Solutions. One is spent each time you submit an answer for grading; a question with several parts spends one per part. Skipping costs nothing.
• Chat messages. One is spent for each message you send the tutor. What the tutor writes on its own — the study advice, the practice-set proposal, the wrap-up — costs nothing.

Both allowances reset every month, on the day of the month your plan started, whether you are billed monthly or yearly. Unused allowance does not roll over. When an allowance runs out, nothing is lost: your account, your history and the answer you were working on stay exactly as they are, and you can either move to a larger plan or wait for the reset.

If an AI evaluation fails through a fault on our side, the solution is returned to your allowance automatically.

Allowances have no cash value, cannot be transferred to another account, sold or exchanged for money.

5. Prices and payment

All prices are shown in US dollars and include any sales tax that applies. The pricing page shows what each plan costs monthly and yearly and what allowances it carries, and the checkout screen shows you the plan and the amount before you pay.

Payment is taken by PayPal, which sends you the receipt. A paid plan is a recurring charge: PayPal charges you again at the start of each billing period — every month, or every year — until you cancel. The price shown when you subscribe is the price that applies; if we change it, we will tell you before the change reaches one of your renewals.

The Free plan costs nothing and needs no payment method.

6. Cancelling and refunds

You can cancel a paid plan at any time, in Settings → Plan or by emailing [email protected] from the address on your account. Cancelling stops the next charge.

• You keep access until the end of the period you have already paid for. When that period ends the account moves to the Free plan. Nothing you have written is deleted.
• Payments already made are not refunded — including a period you did not use, and allowance you did not spend.
• Changing plan starts the new plan straight away and stops the old one.

Nothing here limits any right you have under applicable consumer protection law, including the federal and state consumer statutes that apply to you. Where these terms and that law disagree, the law wins.

7. How you may use the service

Use 2Sigma to study. Do not:

• resell, redistribute or publish the questions, solutions or tutor output;
• scrape the service, or access it through anything other than the interface we provide;
• share an account, or use someone else's;
• try to break, overload or work around the service's limits, or to extract material you have not paid for;
• upload anything unlawful, or anyone else's personal details.

We apply rate limits to keep the service available and to control the cost of AI calls. Hitting them is not a fault.

8. Content

The courses, questions, solutions and everything else we present remain ours or our licensors'. You get a personal, non-transferable right to use them to study for as long as your account is open. Past-exam material is used for educational purposes and remains the property of the institution that set it.

What you write and draw stays yours. You give us the permission we need to store it, show it back to you, send it to our AI provider for grading and tutoring, and use it to run and improve the service — described in full in our Privacy Policy.

9. Availability, changes and termination

We aim to keep 2Sigma available but we do not promise uninterrupted service; we may take it down for maintenance, and we may change or discontinue features.

You may close your account at any time. We may suspend or close an account that breaks these terms, or that we reasonably believe is being used fraudulently. If we close your account without you having broken these terms, we refund the unused part of the period you have already paid for.

We may change these terms. We will post the new version here with a new date, and we will tell you before a change that materially affects you takes effect. If you do not accept a change, cancel your plan and stop using the service.

10. Liability

We provide the service with reasonable care, but as an educational aid and without any warranty that its content or its AI output is accurate or complete. Your results are your own.

To the extent the law allows, our total liability to you for any claim connected with the service is limited to the amount you paid us in the 12 months before the claim. Nothing here excludes liability that cannot be excluded by law, including for death or personal injury caused by negligence, for fraud, or under applicable consumer protection law.

11. Law and jurisdiction

These terms are governed by the laws of the State of Delaware and the federal law of the United States, without regard to conflict-of-laws rules, and the state and federal courts sitting in Delaware have jurisdiction. If you are a consumer resident elsewhere, this does not deprive you of the protection of the mandatory consumer rules of the place you live in.