Privacy Policy

Last updated: September 14, 2026

This Privacy Policy explains how Mathhead, Inc. collects, uses, shares, and protects personal information when you use EulerVertex, our AI-assisted platform for university-level mathematics, available at eulervertex.com (the "Service").

Please read this policy together with our Terms of Service and Refund & Cancellation Policy.

1. Who We Are

EulerVertex is operated by Mathhead, Inc., a corporation organized under the laws of the State of Delaware, United States. For the purposes of the EU and UK General Data Protection Regulation ("GDPR"), Mathhead, Inc. is the controller of the personal information described in this policy.

• Company: Mathhead, Inc.
• Postal address: 1020 Florence Lane, #13, Menlo Park, CA, 94025, USA
• Privacy contact: service@eulervertex.com

The Service is operated from the United States. It is not directed at, or actively marketed in, the European Economic Area or the United Kingdom, but we honor the rights described in Section 9 for any user to whom those laws apply.

2. Information We Collect

2.1 Information you give us

Account information (required to register). When you create an account we collect your email address, a display name, and a password. Your display name is public and your email address is visible to other signed-in users — see Section 4, and pick both accordingly. Passwords are handled by our authentication provider and are stored only as salted cryptographic hashes — we never have access to your plaintext password. We currently support email-and-password sign-in only; we do not offer social or single sign-on login, so we receive no data from any social network.

Optional profile information. You may choose to add, edit, or remove any of the following at any time from your dashboard profile: your institution or organization (free text), a short bio, an ORCID researcher identifier, and an avatar (generated from a stored style seed and appearance options — not an uploaded photograph).

Role requests. If you request an elevated role (for example researcher, instructor, or professional), we collect the role you requested and the written justification you submit, and we retain our reviewer's decision and any review notes.

Communications. If you email us at service@eulervertex.com, we retain your message and our reply.

We do not ask for or store your date of birth, government identifiers, or a residential address. We do not currently collect a telephone number.

2.2 Payment information

Payments are processed by Stripe, Inc., not by us. When you subscribe or purchase credits, you enter your payment details directly with Stripe. We never receive or store your full card number, card expiry, or card security code.

Stripe collects and processes your billing name, billing address, payment card details, and transaction records as an independent controller under Stripe's Privacy Policy. From Stripe we receive and store only a customer and subscription reference, the last four digits and brand of your card, and the status of your payments. In our own records we store your subscription tier and subscription expiry date, which together determine your access to paid content.

2.3 Information created as you use the Service

Using EulerVertex generates a detailed record of your learning activity. We collect:

• Problem attempts — every problem you attempt, the answer you submitted, whether it was graded correct, whether the attempt was rated, and its timestamp. Attempts form an integrity record and, as described in Section 8, are retained rather than edited or deleted individually.
• Ability and difficulty ratings — your overall Elo rating and your per-subcategory Elo ratings, together with the number of rated attempts behind each.
• Quiz and practice sessions — the sessions you start, the problems selected into them, the parameters used, and their status and completion times.
• Curriculum progress — the learning objectives you mark complete within a class.
• Daily problem selections — which daily problem was assigned to you on a given date.
• View history — a short list of content you have recently opened, including each item's title and link. This list is automatically trimmed to your 20 most recent items; older entries are deleted.

2.4 Content you publish or share

The Service is collaborative, and much of what you create is visible to others. We store:

• Discussion content — posts, replies, answers, and comments you write in classes or on content pages, including any post you mark as anonymous. Marking a post anonymous hides your name from other users; it does not make the post anonymous to us, because your account remains associated with it in our records.
• Community solutions — solutions you submit to problems, and whether an instructor adopted one.
• Votes, bookmarks, and collections — the items you upvote, bookmark, and organize into folders.
• Reports and flags — content you report, including your stated reason and any details you add.
• Authored content — nodes, facets, pages, courses, curricula, problems, and problem lists you author, together with their revision history. Authorship is recorded permanently and, for published content, is displayed publicly. See Section 10 of the Terms of Service for what publishing means.

2.5 Class and invitation data

If you join or run a class, we store your class memberships and role (instructor, teaching assistant, or student), who invited you, and when you joined.

If you invite someone to a class by email, we store the email address you provide even if that person never creates an account, along with the invitation's status and expiry, so that we can deliver and validate the invitation. If you received an invitation and do not want us to hold your address, contact service@eulervertex.com and we will delete the invitation record.

2.6 AI tutor and AI authoring assistant

When you use the AI tutor or the AI authoring assistant, we store the full text of your conversation — your messages, the assistant's replies, and a record of any tools the assistant invoked on your behalf, including their inputs and results — so that a conversation can continue across turns.

We also record, for each exchange, how much model capacity it consumed — the model used, the number of input, output, cached, and reasoning tokens, how long the turn took, and whether it completed — together with a running per-user total. We use this to operate the service, size capacity, prevent abuse, and support usage-based pricing. These records describe your usage; they do not contain the text of your conversation.

Three things are worth knowing about this data. First, your messages and the surrounding content context are transmitted to our AI provider, as described in Sections 5 and 7. Second, conversation transcripts and usage records are held in a separate database operated by our tutor service, not in the main account database. Third, that separate database is not erased at the moment you delete your account, but automatically afterwards — see Section 8 for when those records are removed. Do not enter sensitive personal information, credentials, or confidential material into the AI tutor.

AI features require an account. You must be signed in to use the AI tutor or the AI authoring assistant, and your conversations are associated with your account. We do not offer AI features to signed-out visitors, and we do not fingerprint your device or browser in order to provide them.

2.7 Code you submit for execution

Some interactive content lets you run code. When you do, the code and any input you provide are sent to a third-party public code-execution service to be run and the output returned. We relay this request from our servers, so your IP address is not exposed to that service. Do not place personal or confidential information in code you submit.

2.8 Technical and usage data

Our hosting and infrastructure providers automatically log standard technical data, including IP address, browser type and version, device and operating system, referring page, pages requested, and timestamps, for security, abuse prevention, debugging, and capacity planning.

2.9 Analytics

We do not currently use any third-party analytics, advertising, profiling, or cross-site tracking service. We set no advertising cookies and build no advertising profiles.

Our hosting provider collects the standard technical request logs described in Section 2.8, and may provide us with aggregate, cookieless measurement of page views and site performance. This tells us how many people visited a page; it does not identify you.

If we introduce analytics in future, we will update this policy first, and — where consent is required — ask for your consent before any such service is loaded.

3. How We Use Your Information

We use personal information to:

• create and administer your account, authenticate you, and keep you signed in;
• deliver the Service — serve content, run practice and quizzes, grade your answers, calculate and update your Elo ratings, track curriculum progress, and show your recent history;
• operate classes, including rosters, invitations, enrollment approval, and discussions;
• provide AI tutoring and AI authoring assistance;
• process payments, manage subscriptions and credits, apply access tiers, and handle refunds;
• send you service messages — email verification, password resets, class invitations, and notifications about your account or classes;
• review role-upgrade requests;
• moderate content, investigate reports, enforce our Terms, prevent fraud and abuse, and secure the Service;
• measure and improve the Service, including which content is effective;
• comply with legal obligations and establish, exercise, or defend legal claims.

We do not use your personal information to train AI models, and we do not sell your personal information. See Section 7 for what our AI provider may do with data we send it.

Legal bases (EEA and UK users)

Where the GDPR applies, we rely on the following legal bases:

Where we rely on legitimate interests, we have assessed that those interests are not overridden by your rights. You may object at any time — see Section 9.

4. How We Share Your Information Within the Service

Some information is visible to other users by design. This is a function of how the Service works, not a disclosure to third parties.

• Your display name and avatar are public. These two appear wherever your work is attributed — including on pages that anyone can read without signing in, and which search engines may index. They are the minimum needed to credit an author. You can change your display name at any time.

• The rest of your profile requires an account to see. Your email address, institution, bio, and ORCID are visible to other signed-in users of the Service, and to no one else. This is deliberate: EulerVertex is collaborative, and instructors, teaching assistants, and classmates need to be able to identify and contact one another.

  Please read this before you sign up. It means any signed-in user — not only people in your classes — can see the address you register with. If you would rather not share your everyday address, register with one you are comfortable making visible, such as your university address or an alias. You can change the address on your account at any time. Signed-out visitors can never see your email address, and neither can search engines.

• Instructors and teaching assistants. If you join a class, the instructors and teaching assistants of that class additionally see that you are a member, your discussion activity in the class, your progress against the class curriculum, and your work on problems and problem lists assigned within the class. Join a class only if you are comfortable with this.

• Other students in a class. Other members can see your display name and your non-private discussion posts.

• Published content and community contributions. Content you publish, along with solutions, comments, and votes you contribute publicly, is visible to other users and may be visible to the public internet. Your authorship is attributed. Other users may be able to copy or adapt your published content within the Service, as described in the Terms of Service.

• Content you keep personal. Content saved with personal status is visible only to you.

• Administrators. Our staff administrators can access account and content records where necessary to operate, support, moderate, and secure the Service.

Once you publish content or post publicly, others may have already seen, copied, or built upon it. Deleting it later cannot undo that.

5. Service Providers and Third Parties

We share personal information with the following processors and service providers, each only to the extent needed to perform its function:

We may also disclose personal information:

• To comply with law — in response to a valid subpoena, court order, or other lawful request, or where disclosure is required by applicable law.
• To protect rights and safety — where we reasonably believe disclosure is necessary to investigate or prevent fraud, abuse, or a threat to the safety of any person.
• In a business transfer — if Mathhead, Inc. is involved in a merger, acquisition, financing, or sale of assets, personal information may be transferred as part of that transaction. We will notify you and, where required, give you a choice before your information becomes subject to a materially different privacy policy.

We do not sell your personal information, and we do not share it for cross-context behavioral advertising. We do not use your data to serve you targeted advertising.

6. Cookies and Similar Technologies

Strictly necessary. We set a session cookie to keep you signed in. The Service cannot function without it, and it is not used for tracking.

Local browser storage. We store two small values in your browser: the email address you last signed in with (to pre-fill the login form), and which folders you have expanded in the content editor. These never leave your device unless you tell your browser to sync them.

Analytics and advertising cookies. We set none. As stated in Section 2.9, we do not use any third-party analytics, advertising, or cross-site tracking service, so there are no analytics cookies to consent to or opt out of. Any aggregate measurement our hosting provider gives us is cookieless.

Your choices. You can block or delete cookies in your browser settings, though doing so may sign you out. If we introduce analytics cookies in future, we will update this policy and, where consent is required, obtain your consent before setting them — and you will be able to withdraw that consent at any time.

We do not currently respond to browser "Do Not Track" signals, as there is no common standard for them. We do honor Global Privacy Control signals where legally required.

7. AI Processing

The AI tutor and AI authoring assistant are powered by a large language model provided by Google through Vertex AI, called from our own Google Cloud project. When you use these features, your messages and relevant content context are transmitted to that service to generate a response.

Under Google's enterprise terms for Vertex AI, your prompts and the responses generated from them are not used to train Google's general-purpose models. We do not use your conversations to train any model of our own either.

We store your conversation transcripts, and records of how much model capacity each exchange consumed, as described in Section 2.6. Their retention is described in Section 8.

AI output is frequently wrong. Explanations, worked solutions, and generated problems may contain mathematical errors, and automated grading may mark a correct answer wrong or a wrong answer correct. See the Terms of Service for the full disclaimer. Do not rely on AI output as authoritative, and do not enter sensitive personal information into it.

8. Data Retention

We retain personal information for as long as your account is active and thereafter as described below.

Problem attempts. Attempt records support rating integrity and cannot be edited or individually deleted through the Service. They are deleted outright when you delete your account, along with your Elo ratings, quiz sessions, curriculum progress, votes, and class memberships.

AI transcripts and usage records. These live in a separate database operated by our tutor service. They are erased automatically after you delete your account, without you needing to ask: our tutor service regularly checks for deleted accounts and removes the conversations, the assistant's stored session state, and the usage records tied to them, within 30 days of your deletion. What we keep is a running record of what the service cost us, totalled by day, model, and type of allowance. It carries no identifier for any user, no per-conversation times, and nothing you asked or were told.

Published content. If you delete your account, content you published, and contributions such as comments and community solutions that other users have built upon, may remain available to preserve the integrity of discussions and shared material. Where we retain such content, we will disassociate it from your name and profile unless we are required to keep the attribution. If you need specific published content removed, contact us and we will consider the request in good faith.

9. Your Rights and Choices

Everyone. You can view and edit your display name, institution, bio, ORCID, and avatar at any time from your dashboard, and you can change your password or reset it by email.

Deleting your account. You can delete your account yourself, from your dashboard. Deletion is immediate and irreversible, and it acts only on the account making the request. When you delete:

• Your personal data is erased — profile, account record, problem attempts, Elo ratings, quiz sessions, curriculum progress, view history, bookmarks, collections, votes, notifications, and class memberships.
• Content that other people rely on is kept but disconnected from you. Anything you authored or posted publicly — nodes, pages, problems, courses, discussion posts, comments, community solutions, moderation reports — is reattributed to an anonymous "Deleted User" placeholder rather than removed, so discussions and shared material do not break. Your name, profile, and email no longer appear anywhere on it.
• AI transcripts and usage records are erased too, automatically and within 30 days, as explained in Section 8. Only cost totals that identify no one are kept.

If you would rather we handled deletion for you, or you cannot sign in, email service@eulervertex.com from the address on your account and we will verify the request and act on it within the timeframes below.

California residents (CCPA/CPRA)

You have the right to know what personal information we collect, use, and disclose; to access a copy of it; to correct inaccurate information; to delete it; and to be free from discrimination for exercising these rights. We do not sell or share personal information as those terms are defined by the CPRA, and we do not process sensitive personal information for purposes requiring a right to limit.

The categories of personal information we collect are described in Section 2, the purposes in Section 3, the parties we disclose to in Sections 4 and 5, and our retention periods in Section 8.

To exercise a right, email service@eulervertex.com. We will acknowledge within 10 business days and respond substantively within 45 days, extendable by a further 45 days where reasonably necessary. You may use an authorized agent; we will ask for proof of authorization.

EEA and UK residents (GDPR)

You have the right to access your data; to rectify inaccurate data; to erase it; to restrict or object to processing, including processing based on legitimate interests; to data portability; and, where processing is based on consent, to withdraw that consent at any time without affecting prior processing.

Email service@eulervertex.com to exercise any of these. We will respond within one month, extendable by two further months for complex requests. You also have the right to lodge a complaint with your local supervisory authority, or with the UK Information Commissioner's Office.

Everywhere else

If your local law grants you similar rights, contact us and we will honor them to the extent they apply.

10. International Transfers

We are based in the United States and our infrastructure providers process data in the United States and other countries. If you access the Service from the EEA, the UK, or another jurisdiction with data transfer restrictions, your personal information will be transferred to and processed in the United States, which has not received an adequacy decision from the European Commission covering all transfers.

AI tutor requests are routed globally. Our AI provider is configured to serve each request from whichever of Google's regions can answer it, which means the text you send to the AI tutor may be processed in a data centre outside the United States. The same safeguards below apply to that processing.

Where required, we rely on the European Commission's Standard Contractual Clauses (and the UK International Data Transfer Addendum) in our agreements with providers, together with the technical and organizational measures described in Section 11. You may request further information about these safeguards at service@eulervertex.com.

11. Security

We take reasonable technical and organizational measures to protect personal information, including encryption in transit (HTTPS), encryption at rest with our database providers, hashed password storage, row-level access controls in the main account database that restrict each user's data to that user and to those authorized to see it, and restricted administrative access.

The tutor database described in Section 2.6 is reached only by our tutor service, which holds the sole credential for it. It is not directly reachable by users, and you are never issued credentials to any of our databases. Signing in is required before the AI tutor will answer, and each conversation is bound to the account that started it.

No method of transmission or storage is completely secure, and we cannot guarantee absolute security. You are responsible for keeping your password confidential and for all activity under your account. Tell us immediately at service@eulervertex.com if you believe your account has been compromised.

12. Children's Privacy

The Service is intended for university-level learners and educators. You must be at least 13 years old to use the Service, and at least 18 to make a purchase. We do not knowingly collect personal information from children under 13. If you believe a child under 13 has provided us with personal information, contact service@eulervertex.com and we will delete it promptly.

We do not direct the Service to children under 13, and we do not knowingly serve users under that age.

13. Students, Schools, and Institutions

EulerVertex is currently offered directly to individual users. Accounts are created by individuals, and classes are created and run by individual instructors, not by institutions.

We are not currently acting as a "school official" under the U.S. Family Educational Rights and Privacy Act ("FERPA") and we do not receive education records from any institution. If we begin offering institutional accounts under which a school provides us with student records, that relationship will be governed by a separate written agreement with the institution, and we will update this policy before doing so.

If you use EulerVertex in connection with a course, note that your instructor may see the class data described in Section 4. Your institution's own policies may also apply to your use.

14. Third-Party Links

The Service may link to third-party websites and resources we do not control. This policy does not apply to them, and we are not responsible for their content or privacy practices. Review their policies before providing them with personal information.

15. Changes to This Policy

We may update this Privacy Policy from time to time. When we do, we will revise the "Last updated" date above. If we make a material change, we will provide additional notice — by email to the address on your account or by a prominent notice in the Service — before the change takes effect. Continuing to use the Service after a change takes effect means you accept the updated policy.

16. Contact Us

Questions, requests, or complaints about this policy or your personal information:

• Email: service@eulervertex.com
• Mail: Mathhead, Inc., 1020 Florence Lane, #13, Menlo Park, CA, 94025, USA

We will respond as promptly as we can, and within the statutory timeframes in Section 9 where they apply.