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Website & Purchase Terms

Last updated: 31 August 2026

These terms cover two things: using this website (www.soverain.cz), and subscribing to our app Diagon through it. We've kept them short and in plain English — that doesn't make them any less binding, just easier to read.

Who we are

We are Soverain s.r.o., a company registered in the Czech Republic.

  • Company ID (IČO): 29693144
  • Registered office: Chabařovická 1324/21, Kobylisy, 182 00 Praha 8, Czech Republic
  • Commercial Register entry: registered in the Commercial Register kept by the Municipal Court in Prague, file C 450889
  • Email: hello@soverain.cz

In these terms, "we", "us" and "Soverain" mean Soverain s.r.o., and "you" means the person browsing this site or subscribing to Diagon.

What these terms cover — and what they don't

These terms cover:

  • your use of this website, and
  • Diagon subscriptions bought through this website's checkout.

They do not cover:

  • Using Diagon itself. The software is licensed under our End User Licence Agreement (EULA).
  • Kanban+ or anything else we sell on the Atlassian Marketplace. Those purchases are governed by Atlassian's terms and the applicable end-user agreement, not by anything on this page.
  • How we handle personal data. That's covered by our Privacy Policy.

Who you're actually buying from

When you subscribe to Diagon here, checkout is run by FastSpring, our merchant of record. FastSpring is the trading name of Bright Market, LLC (801 Garden Street, Santa Barbara, California, USA) and its affiliates, including FastSpring B.V. (Amsterdam, the Netherlands); the entity handling your purchase is named on your receipt. That means two contracts come into existence, and it's worth being clear about the split:

  1. The purchase contract is with FastSpring. FastSpring charges your payment method — the first time and at every renewal — calculates and handles VAT or sales tax, issues your invoice or receipt, stores your payment details, and processes refunds. That contract is governed by the terms FastSpring presents at checkout, and FastSpring's privacy policy covers what you enter there.
  2. The software licence is with us. Your right to use Diagon comes from Soverain under the EULA. FastSpring resells the subscription; the EULA governs the software.

We never see or store your payment details — those go to FastSpring only.

How subscribing works, step by step

  1. Try Diagon free for 30 days. Download the app and the whole thing works from first run — every feature, including the bundled local AI. No account, no card.
  2. Subscribe when you want to keep it. Clicking "Subscribe" opens FastSpring's checkout. The final price — in your local currency, including any applicable tax — is shown there before you confirm.
  3. FastSpring charges you and emails your invoice or receipt.
  4. We issue your licence key. It's emailed to you and entered once in the app. The key is cryptographically signed and the app validates it offline; it stays valid to the end of the period you've paid for, plus a short grace window, and renews itself automatically whenever the app is online.

Your subscription auto-renews. FastSpring charges the same payment method at the end of every billing period — monthly or yearly, whichever plan you chose — until you cancel. You can cancel at any time in FastSpring's self-service portal: soverain.onfastspring.com/account (enter the email you bought with and a sign-in link arrives), or use the subscription-management link in any FastSpring receipt email. Cancelling stops the next charge; Diagon keeps working to the end of the period you've already paid for.

What a subscription gets you (in brief)

A Diagon subscription unlocks the app — all of it, including the bundled local AI — and includes every update we release while the subscription is active. One subscription covers one person, on any machines they use themselves; teams buy one per person.

When the trial or a subscription ends, the app locks. There is no free tier, and no version of Diagon keeps running once your subscription stops. Your diagrams are plain-text files that stay on your machine and stay readable in any editor — it's only Diagon itself that won't run without an active subscription.

Under Czech digital-content rules (§ 2389a et seq. of the Czech Civil Code), the agreed update period is the period your subscription runs, and we provide updates — including security updates — throughout it. The full licence terms are in the EULA.

Prices and tax

Diagon is EUR 4.99 per month or EUR 49.90 per year (the yearly plan is exactly two months free). Prices are set on this website but finalised at checkout: FastSpring shows the price in your local currency, with any applicable VAT or sales tax calculated and displayed before you pay — first charge and renewals alike. Collecting and remitting tax is FastSpring's job as merchant of record, not ours.

Refunds

Refunds are issued through FastSpring as the seller of record. Our own policy is simple: ask within 14 days of any charge — your first one or a renewal — and you get a full refund, no questions asked. How to ask is described in our Refund Policy.

Consumer information for distance purchases

Buying online is a "distance contract" under Czech and EU consumer law. Because FastSpring is the seller of record, most of the statutory pre-contract information about payment and withdrawal is given to you by FastSpring at checkout and in the terms it presents there. To the extent this information is ours to give as the software provider, here it is:

  • Who we are: see "Who we are" above.
  • What the product is: Diagon is a desktop diagrams-as-code app for Windows and Linux (a macOS build is in development), with an AI model bundled into the app that runs locally on your machine. There is no telemetry, and your diagram text is never sent anywhere. Diagon makes three kinds of network request: a licence check and renewal with soverain.cz; an update check to GitHub, where the releases are published; and, only if you write an image or icon URL into a diagram yourself, a fetch of that image from the host you named.
  • Price: EUR 4.99 per month or EUR 49.90 per year, shown at FastSpring's checkout in your local currency, including applicable tax, before you commit to anything.
  • Duration: a subscription that runs month to month or year to year and auto-renews until you cancel, as described above. Cancel any time via FastSpring's self-service portal; access continues to the end of the period you've paid for. A 30-day free trial comes first, with no account and no card.
  • Withdrawal and refunds: refunds are issued through FastSpring; within 14 days of any charge we refund in full, no questions asked. See our Refund Policy and the terms FastSpring presents at checkout.
  • Conformity: if Diagon is faulty or doesn't match what we've described, you have the statutory rights Czech law gives consumers for digital content. Write to hello@soverain.cz and we'll sort it out. Nothing in these terms limits those rights.
  • Out-of-court dispute resolution: consumer disputes with Soverain about Diagon or the licence can be taken to the Czech Trade Inspection Authority (Česká obchodní inspekce, www.coi.cz), the statutory ADR body for Czech businesses. Disputes about the charge or a refund itself are best raised with us first — we can act on them directly with FastSpring — or with FastSpring's consumer support, as the seller of record.

Using this website

You're welcome to browse the site, download Diagon and subscribe. In return, please don't:

  • attempt to break into, probe or overload the site,
  • use it to distribute malware or anything unlawful, or
  • misrepresent yourself as affiliated with Soverain.

That's it. There's no account system on this site, so there's not much else to regulate.

Our content

The content of this site — text, images and design — belongs to Soverain or its licensors. You may browse the site and download Diagon; beyond that, please don't copy or reuse our content without permission. The software itself is governed by the EULA, not by this section.

We use Diagon and Soverain as the names of our product and our company, and ask that you not use them in a way that suggests we made or endorsed something we did not.

The website itself

We try to keep the site accurate and available, but it's provided as-is: content may change, and the site may occasionally be down. Product descriptions on the site are exactly that — descriptions. The documents that govern a subscription are these terms, the EULA, and the terms FastSpring presents at checkout.

Changes to these terms

We may update these terms from time to time — for example when we launch something new or the law changes. The current version is always at this address, with the date at the top. Changes don't rewrite the past: the terms in force when you were charged are the ones that apply to that billing period.

Governing law

These terms and the EULA are governed by Czech law. If you're buying as a consumer, this choice doesn't deprive you of any mandatory protections of the law of the country where you live. Your purchase contract with FastSpring is governed by the terms FastSpring presents at checkout.

Contact

Questions about this site, these terms, or your subscription: hello@soverain.cz.

For questions about a charge, an invoice, or a refund, start with us — we can see the order in FastSpring and act on it directly — or go straight to FastSpring's consumer support, which holds the payment records.