Privacy Policy

1. Who we are

StiffStruct is a structural-analysis website with a free plan and paid plans. In this policy, “we” means the site owner. Contact details are on the contact page. This policy should be read together with the Terms and Conditions.

2. What we collect

• Nothing, if you do not sign in. You can open the calculator, build models and run analyses without giving us any personal information.
• If you sign in: sign-in is provided by Google Firebase Authentication, either with your Google account or with an e-mail address and password. Firebase stores your e-mail address, your display name (and profile picture link, if your Google account provides one), an internal account identifier, and basic sign-in records such as the time of your last sign-in. We never see or store your password: for e-mail accounts Firebase keeps only a secure hash of it. Firebase also sends account e-mails on our behalf, such as address verification and password-reset messages.
• If you start a trial or buy a plan: see section 3. We receive only your subscription status, plan and country, together with the e-mail address of your account.
• If you write to us: your message and e-mail address, which we use to reply. The contact form only opens your own e-mail app; it does not send data to our servers.
• Technical data: like any website, the host that serves the pages and the content delivery network may process your IP address and browser details in their server logs to deliver the files and keep the service secure.

3. Payments and subscriptions

Payments are handled by Dodo Payments, which acts as the merchant of record: it sells the plan to you, takes the payment and collects the tax. When you start a free trial or buy a plan, you enter your card or other payment details, your name and your billing country (and an address or tax number if you add them) on the payment page of Dodo Payments, which processes them under its own privacy policy.

• What we receive from the payment provider: your subscription status (for example trial, active or cancelled), the plan and billing interval, the trial and period end dates, your country, an order identifier and your e-mail address. We never see your full card number.
• Subscription records: we store this status in Google Firebase (Firestore) against your account, so the calculator can unlock the features you have paid for. Only you can read your own record, and it can be written only by our payment service, not by the browser.
• Payment service: a small service that receives notifications from Dodo Payments and updates your record runs on Cloudflare.

4. Your models

Models, load cases, units and results are created and processed in your browser. The autosave is kept in your browser’s local storage and is not uploaded. A share link contains the model inside the link; whoever receives or finds the link can open that model, and the link may be stored by the services you paste it into (for example e-mail or chat). Do not put confidential information into a model you plan to share.

5. Cookies and local storage

We do not use advertising, analytics or tracking cookies. The Service stores the following on your device:

• Local storage: your model autosave, panel sizes, and preferences such as theme (auto, light or dark), high-contrast text, units and number of decimals. These stay on your device and you can clear them in your browser settings.
• Sign-in storage: if you sign in, Firebase Authentication keeps a token in your browser (in local storage or IndexedDB) so that you stay signed in until you sign out.

6. How we use information

We use account information only to run sign-in (to show detailed values), to unlock the plan you have chosen, to understand roughly how many people use the Service, to keep the Service secure, to answer your messages, and to deal with billing questions and refunds. We do not use it to profile you or to send marketing e-mail.

7. No selling of data

We do not sell, rent or trade your personal information, and we do not share it with advertisers.

8. Third-party services

• Dodo Payments, our payment provider and merchant of record, which receives your payment details and billing information (section 3) and keeps transaction records as the law requires.
• Google Firebase (Google LLC): Authentication for sign-in, and Firestore for your subscription record. Google processes this data under its own privacy policy and the Firebase terms.
• Cloudflare, which runs our payment service (it receives notifications from Dodo Payments) and may also serve the website.
• jsDelivr content delivery network, which serves software libraries (three.js, KaTeX, Pyodide). Your browser contacts it directly when those features load, and it can see your IP address.
• The web host (for example GitHub Pages or Cloudflare Pages), which serves the website files and may keep standard access logs.

We are not responsible for how these services handle data, so please read their policies if you are concerned.

9. Retention and deletion

Local data stays on your device until you clear it. Account data stays with Firebase until you ask us to delete the account. Subscription records are kept while the account exists, and payment and invoice records are kept by Dodo Payments and by us for as long as tax and accounting law requires, even after an account is deleted. To delete your account and its data, send a request from the e-mail address on the account through the contact page; we will delete it within a reasonable time. Messages you send us are kept only as long as needed to answer them and keep a record of the conversation.

10. Your choices and rights

You can use most of the Service without signing in, clear your local data at any time, sign out at any time, and ask us to access, correct or delete the personal data we hold about you. Depending on where you live, you may have additional rights under data-protection law (for example in the EU, the UK or California), such as objecting to processing or lodging a complaint with your local authority. Contact us to exercise any of them.

11. Children

The Service is a general educational tool and is not directed at children under 13. If you believe a child has created an account, contact us and we will delete it.

12. Changes

We may update this policy. The “Last updated” date at the top shows the current version, and significant changes will be made visible on the website.

13. Contact

Privacy questions or requests: use the contact page or write to the contact address.