Keep Mermaid but fix the layout.
Your AI agent writes great Mermaid. Default viewers render it badly. line9 is a new engine for the same syntax — superior layout, presentation-ready type, no markup changes.
Render Mermaid straight from your terminal, and give your AI agent a render tool it can call.
curl -fsSL https://line9.ai/install.sh | sh 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.
One clear primary flow
The main line stays straight and central; the side branches resolve around it instead of fighting for the middle. You read the shape of the workflow before you read a single label.
Why line9
Layout that argues.
Intelligent placement, honest orthogonals, crossings minimised. Diagrams read like they mean it — no manual pushing of boxes.
Legible at any size.
Scale a diagram down to fit and the labels stay readable — line9 keeps a companion table of node names alongside, so you never trade away the structure or the detail.
Type, not decoration.
Themes designed as typography, not palettes. Export to SVG, PNG, and PDF with the same care a typesetter would bring.
How it works
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.
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.
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.
Render from your terminal
line9 isn’t the AI. It’s the rendering substrate.
Every other AI-diagram tool bolts on its own model, blind to your code. line9 is the
renderer for whatever agent you already use — Claude Code, Cursor, Copilot. It shells out
to line9 render, the diagram opens in
a browser tab, and re-runs update the same tab live. Free for personal use, nothing to
start.
curl -fsSL https://line9.ai/install.sh | sh Windows, Homebrew & more on the CLI page.
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
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
Commercial use, published diagrams, premium themes.
- ·Commercial-use CLI for agent and CI workflows
- ·Watermark removal and premium curated themes
- ·Private workspace + permanent share URLs
See full pricing → $12 / seat for early adopters — locked in while it lasts.
We’re not the only ones who noticed
“The layout is really bad, not the resolution.”
“My hunch is someone needs to vertically integrate to nail this — and it’s a deep one.”
LLMs turned Mermaid into the default way millions of engineers get a diagram — a fast-growing audience that never chose the format, compares it to Lucidchart and slides, and finds the output wanting. line9 closes that gap without changing a line of syntax.
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.
- 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, published share URLs, and premium themes.
- Does my diagram leave my machine?
- No. The CLI renders locally — nothing about your diagram is uploaded when you render it. The cloud only ever holds the diagrams you explicitly choose to publish, and there is no telemetry on free installs.
- Which diagram types are supported?
- Flowcharts get the full line9 layout engine today. 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?
- Your agent writes Mermaid as usual, then calls `line9 render`; the diagram opens in a browser tab and updates live as the agent iterates. `line9 bootstrap` wires it into Claude Code and Codex so the agent knows to use it.
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.
curl -fsSL https://line9.ai/install.sh | sh