Pricing
The web editor is free. The desktop app is a subscription, and every copy starts with a 30-day trial with everything unlocked and no card.
Web editor
Free
- The editor with live preview, for PlantUML, Markdown and D3
- Every template, 109 of them
- Rendering in the browser: your diagrams are never uploaded
- Works on files in folders on your own disk
- Export to SVG and PNG
Desktop
30-day free trial with everything unlocked. No card, and nothing renews on its own.
Two licences for the same software. Choose by how you use it.
Personal
£5.99 a month
For your own projects. Not for commercial use.
Use on 2 computers
Checkout opens at launchBusiness
£9.99 a month
For commercial use: at work, for a company, or for clients.
Use on 2 computers
Checkout opens at launchEverything in the web editor, plus:
The agentic builder
Add elements from a palette, edit them in an inspector, and see which exits you never modelled and which requirements nothing enforces.
The threat register
A STRIDE threat model generated from the trust boundaries and data flows already in your C4 diagram, with severity badges on the diagram and a decision recorded per threat.
Boards, the Planner and local history
Plan the work beside the architecture, and get back any version of a file without having committed it anywhere.
Claude, working in your repositories
Every Claude Code session on your machine can validate, render and open diagrams through Gnomon, and sees what you have open.
A native app that works offline
Faster rendering, the file tree, a terminal, and nothing that needs a browser tab.
Checkout and VAT are handled by Lemon Squeezy, our merchant of record. Your licence key arrives by email; paste it into Settings → Licence.
Questions
What happens when the trial ends, or if I cancel?
Your diagrams are plain files on your own disk, and nothing about a subscription changes that. The desktop app will always open, render and export them, subscribed or not, and the web editor edits them for free. Threat decisions you recorded are kept, so subscribing again brings the register back exactly as you left it.
Do I need a card for the trial?
No. The trial starts the first time you open the app and there is nothing to sign up for. When it ends, nothing is charged; you choose whether to subscribe.
Does the desktop app need an internet connection?
Only to check the licence, once a day when a connection is available. A successful check covers two weeks with no connection at all, and nothing tells you it is happening. A long flight, a captive portal or a machine kept off the network for sensitive work is fine.
What does activation send?
Your licence key and your computer's name, so you can tell your machines apart when moving a licence between them. Your diagrams and files are never sent anywhere.
Which plan do I need?
Personal, for anything you do for yourself. If the work is commercial, meaning you are paid for it, it is done for an employer or a client, or it is used by a business, you need Business. The software is identical; only the licence differs.
How many computers can I use?
Each plan covers 2 computers. Remove the licence from one computer in Settings → Licence to move it to another.