SOVERAIN
Menu
hello@soverain.cz

Diagon End User Licence Agreement

Last updated: 9 October 2026

Changed on 9 October 2026 for Diagon 1.3.0: the app no longer contains an AI model, so the sections that mentioned one were changed to match, and section 8b, on AI assistants you connect yourself, is new.

This agreement (the "EULA") is between you and Soverain s.r.o. It covers Diagon, our desktop diagrams-as-code app. We have kept it short and in plain English on purpose — but it is a real, binding agreement.

The short version: every feature is free for 30 days from first run; after that Diagon needs an active subscription to run; one subscription covers one person on all their machines; your diagrams are plain-text files that stay yours, and Diagon never uploads them anywhere. An AI assistant you choose to connect is your own software, and what it reads goes to its provider (section 8b).

1. Who this agreement is between

Soverain s.r.o. ("Soverain", "we", "us"), IČO 29693144, registered office Chabařovická 1324/21, Kobylisy, 182 00 Praha 8, Czech Republic, registered in the Commercial Register kept by the Municipal Court in Prague, file C 450889. Contact: hello@soverain.cz.

You — the person using Diagon, whether for yourself or on behalf of a company. If you use Diagon for a company, you confirm you are allowed to accept this EULA for that use.

About purchases. Diagon subscriptions are sold through FastSpring (Bright Market, LLC d/b/a FastSpring, USA, with its affiliates, including FastSpring B.V. in the Netherlands), who acts as Merchant of Record. FastSpring runs the checkout, charges you, handles VAT/sales tax, issues your invoice or receipt, and pays out refunds, under the terms it presents at checkout. FastSpring handles the purchase; this EULA governs the software.

What this EULA does not cover. This EULA applies to Diagon only. Our Jira apps, Kanban+ and OnTask, are sold exclusively through the Atlassian Marketplace under the end user agreement elected on their Marketplace listings — nothing here applies to them.

2. Acceptance

By installing or using Diagon, you accept this EULA. If you do not agree with it, do not install Diagon, or uninstall it.

3. The 30-day trial

Diagon is free to download, and the first 30 days from your first run are a full trial: every feature. No account, no card.

When the trial ends, Diagon locks until you start a subscription. There is no reduced free tier — but there is also nothing to rescue. Your diagrams are plain-text files on your own disk, readable and editable in any text editor, with or without Diagon.

Diagon does not upload your content anywhere, and it collects no telemetry of any kind. Diagon makes three kinds of network request, and none of them carries your diagram text:

  • a licence check and renewal to soverain.cz;
  • an update check to GitHub, where the releases are published, which sends nothing about your machine, your licence or your diagrams;
  • and, only if a diagram contains an image or icon URL — one you wrote, or one written into it by an AI assistant you connected (section 8b) — a fetch of that image from the host the URL names.

An AI assistant you connect yourself is a separate matter: it can read the diagram you have open, and it sends what it reads to its own provider. That connection is off until you switch it on. Section 8b covers it.

4. Your licence

When you subscribe, Soverain grants you a non-exclusive, non-transferable licence to use Diagon for as long as your subscription is active, on these terms:

  • Per person. One subscription covers one person. That person may install and use Diagon on any machines they use themselves. For team use, buy one subscription per person.
  • Personal or company use. Both are fine under the same subscription.
  • The whole app. A subscription unlocks all of Diagon. Nothing is held back for a higher tier.
  • It renews automatically. EUR 4.99 per month or EUR 49.90 per year (exactly two months free). It renews until you cancel. FastSpring charges your payment method and stores those details — we never see them.
  • Cancel whenever you like. Cancel through FastSpring's self-service portal at soverain.onfastspring.com/account, or the subscription-management link in your FastSpring receipt emails. Your access runs to the end of the period you have already paid for.

5. What the subscription includes — and what happens when it ends

This is the heart of the deal, so here it is spelled out:

  • While it is active. You get every version of Diagon we release, including all feature and security updates. There is no upgrade fee and no separate "updates year" to keep track of.
  • When it ends, the app locks. Whether you cancel, a payment fails, or you simply stop paying, Diagon stops running once your paid period and its short grace window are over. We would rather write that plainly than imply otherwise.
  • Your files are never touched. Locking is about the app, not your work. Diagon does not delete, move, encrypt, or alter any file of yours. Your diagrams are plain text, they stay exactly where you saved them, and any text editor can open them — with or without a subscription.
  • Coming back is easy. Subscribe again at any time and the same installation unlocks with your new key. Nothing is lost in the meantime.

Example: subscribe on 3 August 2026 on the yearly plan and Diagon runs, fully updated, until you cancel. If you cancel effective 3 August 2027, the app runs to that date and then locks — while every diagram file you made stays on your disk, readable as ever.

6. Licence keys

After you subscribe you receive a cryptographically signed (Ed25519) licence key by email, sent from noreply@soverain.cz. You enter it once. The app checks the signature on your own machine — there is no account to create and no server to log into. The key is tied to the buyer's email so we can help you with support.

  • Valid for what you have paid for. A key is valid to the end of your current billing period plus a 3-day grace window, and it renews itself automatically whenever the app is online. If a machine is offline across a renewal, connect it once and the key refreshes.
  • Your key is non-transferable. Keep it private; do not publish it or share it beyond the person it was issued to.
  • If a key is publicly leaked or widely shared, we may revoke it, and Diagon will stop accepting it.
  • Locking never reaches your files. An expired or revoked key stops the app from running and does nothing else. Diagon sends us no diagram content and gives us no mechanism to read, alter, or delete your documents — and we will not build one.

7. What you may not do

  • Redistribute, resell, or rehost the app.
  • Circumvent, remove, or tamper with the licence check, a licence key, or the 30-day trial period.
  • Reverse engineer, decompile, or disassemble Diagon, except to the extent applicable law expressly permits this despite the restriction (for example, EU interoperability rights).
  • Share, sell, or publish licence keys.

8. Your content is yours

You own your diagrams. Soverain claims no rights of any kind over your content, during a subscription or after one — and none over what an AI assistant you connect writes into a diagram, which is governed by your agreement with that assistant's provider (section 8b). (Diagon never sends your content to us, so we never see it anyway.)

Diagon itself — the app and its code — remains the property of Soverain and its licensors.

8a. Open-source components

Diagon includes open-source components — among them Electron, Chromium and Node.js — each used under its own licence. The full list, with the licence texts, ships with the app as THIRD-PARTY-NOTICES.txt and is installed alongside it.

Those licences govern those components. Where a component's own licence grants you a right — including to copy, modify, reverse engineer, relink or redistribute that component — nothing in this EULA takes that right away, and section 7 does not apply to it. In particular, Diagon dynamically links FFmpeg under the GNU LGPL v2.1, and you may reverse engineer Diagon to the extent necessary to modify that library and relink it for your own use.

The restrictions in section 7 apply to Diagon, which is Soverain's own work.

8b. AI assistants you connect

Diagon contains no AI model. It can be connected to an AI assistant that you already run on the same computer, so that the assistant can read the diagram you have open and draw or change it in your Diagon window. The connection is off until you switch it on, and you can switch it off again at any time.

Any such assistant is third-party software that you choose and run. Soverain does not supply, host or control it. Your use of it, and what it produces, are governed by your own agreement with its provider — not by this EULA. What the assistant reads from your diagram, it sends to that provider; Diagon does not send it anywhere, and Soverain never receives it.

Soverain is not responsible for what an assistant writes into a diagram, or for what the assistant or its provider does with what it reads.

9. Updates and Czech digital-content rules

Czech law on digital content (§ 2389a et seq. of the Civil Code) requires us to provide updates for an agreed period. The agreed update period is the whole time your subscription is active, for as long as you keep renewing. During it, we will provide the updates — including security updates — needed to keep Diagon working as described.

Diagon is supplied as a subscription, not as a one-off copy: when the subscription ends, so do the updates and your right to run the app. Your documents are not part of that. They are your own plain-text files, they stay on your machine, and they remain fully usable without Diagon.

10. Warranty and liability

If you are a consumer, you have statutory rights — including remedies for defective digital content — and nothing in this EULA reduces them.

Beyond what mandatory law requires: Diagon is provided as-is, and we do not promise it is error-free or fit for a particular purpose. A diagram written by an AI assistant you connect can contain mistakes — please review it before relying on it (section 8b).

To the extent permitted by law, our total liability under this EULA is limited to the amount you paid for Diagon in the 12 months before the claim arose. Nothing in this EULA excludes or limits liability that cannot be excluded under applicable law (for example, liability for intentional wrongdoing or harm to health).

11. Term and termination

This EULA applies from the moment you install or first use Diagon and lasts as long as you use it — through the trial, through each subscription period, and after one ends. You can end it at any time by cancelling your subscription and uninstalling.

We may terminate your licence if you materially breach this EULA (for example, by redistributing the app or publishing your licence key) and, where the breach can be fixed, you do not fix it within a reasonable time after we ask. If your licence is terminated for breach, you must stop using Diagon and your licence key. Termination never affects ownership of your own content: your files stay yours, stay where they are, and stay readable.

12. Changes to this EULA

We may update this EULA. If a change affects the price, what your subscription includes, or your rights under it, we will email you before it takes effect and the change will apply from your next renewal — never in the middle of a period you have already paid for. If you do not accept it, cancel before that renewal.

13. Governing law and disputes

This EULA is governed by Czech law. If you are a consumer, this does not deprive you of the mandatory consumer protections of the country where you live, and you may rely on the courts available to you under that law.

Consumers may also use out-of-court dispute resolution through the Czech Trade Inspection Authority (Česká obchodní inspekce, www.coi.cz).

For questions about a payment, billing, invoices, or refunds, email hello@soverain.cz — we can act on the order directly with FastSpring — or contact FastSpring's consumer support; refunds are paid out by FastSpring under our Refund Policy. Within 14 days of any charge — a first payment or a renewal — we refund it in full, no questions asked. That is on top of, and does not limit, any statutory withdrawal right you have.

14. Contact

Soverain s.r.o. — hello@soverain.cz — www.soverain.cz

For how we handle personal data (your email and, if provided, your name — received from FastSpring to issue your licence key and provide support), see our Privacy Policy.