01
Usable layout, automatically.
Carefully placed nodes, shorter arrows, fewer line crossings. Diagrams you can read and share — without twenty minutes of clicking and dragging.
Mermaid diagrams, only better
…a machine you can follow.
Mermaid with Line9
Before & after
Compact, not sprawling
Mermaid stretches the auth flow into one long, thin ribbon you have to scan end to end. line9 folds the same source into a tight block your eye takes in at once — same diagram, a fraction of the space.
Why Line9
02
Legible on a screen or page.
Aspect ratio is a goal. Flowcharts that: 1) fit on a page and 2) stay large enough to read. Get both, simultaneously.
03
Type, not decoration.
Themes designed as typography, not palettes. Export to SVG and PNG with the same care a typesetter would bring.
How it works
- 01
You (or your agent) write Mermaid.
The same .mmd you already write. Nothing new to learn, nothing to migrate — Line9 reads the format AI tools already speak.
- 02
We parse it with Mermaid's own parser.
Line9 uses Mermaid to understand your source, then discards its rendering pipeline entirely. Identical input, completely different engine.
- 03
Our engine lays it out from scratch.
Placement, orthogonal routing, semantic styling and type — composed for legibility, not for a 2012 layout algorithm. Paste and render in five seconds, no login.
How to use Line9
1 Paste
View a diagram you already have
Have some Mermaid diagrams already? See them with Line9’s readable and stylish rendering by pasting your text directly into the diagram editor page.
2 Write
Create a new diagram by hand
Open the diagram editor page and write Mermaid source text into the text panel: your diagram will appear as you go.
3 Generate
Powerful AI diagram creation
Creating flowchart diagrams with AI is made possible by an AI agent running locally alongside Line9’s new CLI tool.
Free CLI · no signup · macOS · Linux · Windows
Render from your terminal
free · cli · agents
Line9 isn’t the AI. It’s the renderer your AI needs.
AI models in the cloud don’t natively have access to your private data and context; they’re
blind to your code. Line9 complements the AI that you already use — Claude Code, Cursor,
Codex, etc. With your agentic AI and Line9’s CLI, you have all you need to create relevant,
detailed and ready-to-use diagrams — quickly and easily. Your AI generates the Mermaid and
shells out to line9 render, the diagram opens in a
browser tab, and edits by the AI update the same tab live.
Render Mermaid straight from your terminal, and give your AI agent a render tool it can call.
Install on macOS / Linux
curl -fsSL https://line9.ai/install.sh | sh Windows, Homebrew & more on the CLI page.
local-first · explicit publish
Your diagrams stay yours
-
Renders on your machine.
The CLI renders client-side through a transient local server. Nothing about your diagram leaves your machine when you render it.
-
Nothing kept unless you say so.
Your .mmd files are the source of truth. The cloud only ever holds the diagrams you explicitly publish — and you can take them down.
-
No login to try, no telemetry on free.
The web viewer needs no account. The free CLI sends no usage data. Evaluate the whole thing without handing anything over.
Pricing
Free
$0 forever, no card
The web viewer plus a personal-use CLI.
- ✓Full custom rendering and every standard theme
- ✓SVG / PNG export, URL-hash sharing
- ✓Personal-use CLI — watermarked, no signup
Pro
$24 per seat / month
Commercial use, published diagrams, watermark removal.
- ✓Commercial-use CLI for agent and CI workflows
- ✓Watermark removal on every export
- ✓Private workspace + permanent share URLs
See full pricing → $12 / seat for early adopters — locked in while it lasts.
credit · independence
Built on Mermaid
Mermaid isn't ours. It's an excellent open-source project and it won for good reasons: text is version-controllable, it goes in any document, and an AI can write it fluently.
Mermaid already solved describing a diagram. Line9 is about drawing it.
Line9 is an independent project, not affiliated with or endorsed by the Mermaid project or Mermaid Chart.
Questions
- Do I have to change my Mermaid?
- No. Line9 reads the exact same Mermaid syntax your tools already write — same .mmd source, no new format, nothing to migrate. You point it at your diagram and get a better render.
- Is this just restyling, or actually different?
- It's a new layout engine. Line9 uses Mermaid's own parser to read your diagram, then discards Mermaid's rendering pipeline and lays the diagram out from scratch — placement, edge routing, and typography. Restyling can't fix a bad layout; re-laying it out can. See it side by side: vs mermaid.live →
- Is Line9 free?
- Yes. The web viewer is free with no signup, and the CLI is free for personal use. Pro ($24/seat, or $12 for early adopters) adds commercial use, watermark removal, and published share URLs (premium themes are coming soon).
- Does my diagram leave my machine?
- The web viewer renders in your browser and the CLI renders on your machine — those diagrams are not uploaded to render them. If you connect Line9 through an AI assistant (MCP), the assistant sends source to mcp.line9.ai to render; that path is described on the MCP docs. The cloud only stores diagrams you explicitly publish. How Line9's MCP handles your data →
- Which diagram types are supported?
- Flowcharts get the full Line9 layout engine today, with sequence diagrams next. Any other valid Mermaid diagram still renders through Mermaid’s own output with a clear badge, so every diagram you have works from day one.
- How does it work with my AI agent?
- Coding agents in a terminal use the CLI: `line9 render` opens a live-updating browser tab, and `line9 bootstrap` wires Claude Code and Codex. ChatGPT, Claude, Cursor and VS Code can use the hosted MCP server instead, so the diagram appears inside the conversation. Add Line9 to your assistant →
Stop hand-fixing your diagrams.
Paste your Mermaid into the viewer, or install the CLI and wire it into your agent. Both are free to start.
Open the viewer →
curl -fsSL https://line9.ai/install.sh | sh