A closed visual feedback loop.
The assistant sees its own output and corrects it. Declarative tools render at the end, into a black box, with nothing to nudge.
Diagrams your assistant can actually see.
Shapes, connectors and labels on a fixed page, stored as SVG, exported to PNG or PDF — built by describing them, in a desktop app or right inside Claude Code.
One-time fee. No subscription. Runs on your machine, with your own Anthropic API key.
A closed visual feedback loop.
render hands back a PNG. An assistant sees that a label overflows or an arrow crosses a
box, and issues a correcting edit. Declarative tools offer no addressable object to nudge
and no way to look at the result.
There is no human in that loop.
Why not Mermaid or D2?
Those are better tools for a plain hierarchical DAG, and an assistant writes them more fluently than it will ever write a bespoke API. This exists for three things they structurally cannot do.
Exact page fit.
Every declarative tool sizes the canvas to its content. This one owns the page — 1008 x 612 points, always — and reports anything that runs off it.
Stable identity.
If slide 7 is slide 6 plus one box, you get literally slide 6's geometry plus one box, not a re-layout that reshuffles everything.
How it works
Buy once, download.
Polar takes the payment and emails you a licence key and the installer link.
Enter two keys.
Your licence key, and your own Anthropic API key. The second one is stored in your OS keychain and is billed to you by Anthropic, not by us.
Describe a diagram.
Type it in the desktop app, or ask for it in Claude Code. The assistant builds it, renders it, looks at the result, and fixes what it got wrong.
Your key, your account, your rate limits. There is no per-diagram markup, because there is nothing of ours between you and the model.
Two ways to use it
The desktop app
You talk to Claude in one pane and the diagram appears in the other, updating after every operation, with SVG, PDF and PNG export and a live token-and-cost meter.
Auto picks a model and an effort level per message, so a first diagram gets the strong model and "make that box blue" does not. Plan gates structural changes on a plan you approve first.
The MCP server
Ten tools, driven from Claude Code or any MCP client. --allow-dir is repeatable and
confines every path the server will touch.
apply_ops is the one that matters — it builds a whole diagram in a single atomic call,
with later operations naming elements earlier ones created. Either every op lands or none
does, so a failure never leaves half a diagram behind.
claude mcp add diagram-builder --scope user -- \
diagram-builder mcp --allow-dir ~/coursesThings it has drawn
The details that stop it being a toy
- The
.svgis both the deliverable and the database — the scene graph lives in the file's metadata block. - Placement resolves once.
--right-of acomputes an absolute position; there is no constraint solver to debug. - A palette name sets three colours — fill, stroke and readable text — and every combination clears WCAG AAA.
- PDF export is true vector, with selectable and searchable text. The fonts are embedded.
- Eight shapes: rect, stadium, ellipse, diamond, cylinder, hexagon, triangle and note.
- Every warning names a concrete fix, like
set width >= 200 or font-size <= 9. - One self-contained binary. No Node, no headless browser, no JVM, no Graphviz.
One price, once.
No subscription, no seats-per-month, no per-diagram fee. You bring your own Anthropic API key, so the only recurring cost is the one you already have with Anthropic.
Personal
$49 once
One person, as many machines as you use.
1 seat
- The desktop app and the MCP server
- Twelve months of updates
- Perpetual licence — it keeps working afterwards
- Email support
Available soon — we are finishing payment setup.
Team
$199 once
Five people, one invoice.
5 seats
- Everything in Personal, five times over
- Five licence keys, managed from one place
- Twelve months of updates
- Perpetual licence — it keeps working afterwards
Available soon — we are finishing payment setup.
One-time payment, not a subscription. Prices are in USD, plus VAT or sales tax where applicable. You will need your own Anthropic API key, which Anthropic bills you for separately. Your licence key and download link arrive by email immediately after payment.
Questions
Is this a subscription?
No. You pay once and the licence is perpetual. It includes twelve months of updates; after that the version you have keeps working forever, you just stop getting new ones unless you buy again.
Do I need an Anthropic API key?
Yes, and you supply your own. It is stored in your operating system's keychain and used directly from your machine. Anthropic bills you for the usage. That is the reason there is no per-diagram fee here — there is nothing of ours sitting between you and the model to charge for.
Where do my diagrams go?
Nowhere. They are ordinary .svg files in a folder you choose. You can open them in
Inkscape, commit them to git, or delete them. Nothing is uploaded to us, because there is no
"us" in the data path — the site you are reading has no database at all.
What is the difference between the desktop app and the MCP server?
They are two front ends onto the same engine, and you get both. The desktop app is a chat window beside a live preview. The MCP server plugs into Claude Code or any other MCP client, so you can ask for a diagram in the middle of doing something else. The desktop app actually drives the MCP server as a child process, which is what stops the two halves drifting apart.
Which platforms?
macOS (Apple Silicon and Intel), Windows, and Linux.
Can I use one licence on more than one machine?
Yes. A seat is a person, not a device. Install it on your laptop and your desktop; just do not share the key with a colleague — buy the Team tier for that.
What if it does not work for me?
Ask for a refund within 14 days and you will get one. See the refund policy.
Who am I actually buying from?
Polar, acting as merchant of record. They handle payment, VAT and sales tax, and the invoice, and they are who appears on your card statement. Cloud Contraptions LLC makes the software.
Buy it once. Run it locally. Keep it.
A perpetual licence with twelve months of updates. If you stop paying attention after that, the version you have keeps working.