What you actually get.

This is the part most tools bury at the bottom.

Everything you write here is Mermaid source — the same text any other Mermaid tool reads. Export SVG or PNG straight from the browser, or PDF from the server, or copy the source out and never speak to us again. There is no proprietary format to be trapped in, because we did not invent one.

The same goes for the model. Bring your own Anthropic, OpenAI or OpenRouter key and the AI bill is between you and your provider — we do not sit in the middle of it, and we do not meter it. The key is encrypted at rest with Fernet and you can delete it whenever you like.

Everything below is in the product now.

21 Mermaid diagram types

Flowcharts, sequence, class, state, ER, Gantt, pie, git graph, user journey, quadrant, mindmap, timeline, XY chart, sankey, block, kanban, packet, C4, requirements, architecture and radar — each seeded into your library as a worked example rather than an empty file.

Browser-side rendering

Mermaid runs client-side. There is no render server and no round trip, which is also why SVG and PNG export happen in the tab you are already looking at.

Bring your own model

Anthropic, OpenAI or OpenRouter — OpenRouter alone reaches a hundred-plus models through one key. A key you brought skips our AI quota entirely.

AI that edits, not just drafts

Describe a change to a diagram you already have and apply the result to the editor in one click. The assistant asks clarifying questions before it guesses.

MCP server, 9 tools

List, read, create, update and search diagrams, generate one from a prompt, ask which engines this instance renders, and pull from Mermaid Chart — over Bearer auth with bcrypt-hashed keys, on your account and your limits.

Import from Mermaid Chart

Paste a read-only token and Diagraff copies your projects and documents across in one pass. Nothing is written back, and you can re-run it.

Teams and sharing

Shared diagram spaces with role-based access, invitations, and public share links for any single diagram.

Self-hostable, MIT

One Linux box, one Python service, SQLite or Postgres. No render sidecar. The license covers the whole application, including the AI wiring and the MCP server — not a core with the useful parts sold back to you.

Live editor

Real-time preview with pan and zoom, folders, dark and light themes that the diagrams follow, and a REST API with keys.

Three ways to pay, and one of them is nothing.

Self-host and you pay us nothing, ever — just your host and your model provider. Bring your own key on the free tier and the AI bill stays at your provider's price with nothing added on top. Hosted is $10 a month, or $96 a year, and we run it for you.

The free tier is 5 diagrams and needs no card. Pro raises that to 1,000 and adds PNG export, team spaces and the REST API.

People who already think in boxes and arrows.

Engineers documenting a system, founders mapping a process, teams that want the architecture diagram to live in version control rather than in a screenshot in a chat thread. If you have ever written Mermaid in a README, this is the tool that stops you doing it in a text box with no preview.

And if you would rather not write it at all, describe the diagram and let a model draft it — on your key, at your provider's price.