Line9 vs mermaid.live
Line9 is a new rendering engine for Mermaid — same syntax, dramatically better layout and typography. mermaid.live is the familiar online editor for stock Mermaid. If your flowcharts look tangled, sparse, or hard to present, the difference is the engine — not the language.
Below is one curated authorization flowchart. The left pane is stock Mermaid (the same layout family mermaid.live uses). The right pane is Line9. No source changes between them.
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Download a single before/after image — stock Mermaid and Line9 side by side, with labels and the line9.ai watermark. Composition runs entirely in your browser.
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Export unlocks when both engines finish rendering.
Want your own diagram side by side? Open the interactive compare page or paste into the free editor.
mermaid.live is the widely used browser playground for Mermaid: type or paste diagram source, see Mermaid’s default render, export from the editor. It is an excellent place to learn Mermaid syntax and to check that a diagram parses. Its layout quality is Mermaid’s layout quality — the same Dagre/ELK-based pipeline most “Mermaid websites” share.
Line9 keeps that Mermaid source and replaces the layout step for flowcharts. It uses Mermaid’s own parser, then rebuilds placement, edge routing, and type from scratch. The product surfaces are a free web viewer/editor at line9.ai/diagram, optional published share URLs, and a CLI for local and agent-driven workflows. Line9 is not a new diagram language and not a fork of Mermaid syntax.
In short: mermaid.live answers “does this Mermaid work?” Line9 answers “can I show this flowchart without hand-fixing the layout?”
| Aspect | mermaid.live | Line9 |
|---|---|---|
| What it is | Official online editor/viewer for Mermaid diagrams | New rendering engine for the same Mermaid syntax |
| Syntax | Standard Mermaid | Standard Mermaid — no new format, nothing to migrate |
| Layout engine | Stock Mermaid (Dagre/ELK-based pipeline) | Line9 layout engine for flowcharts; other kinds via Mermaid |
| CLI | Not a first-class local CLI product | line9 CLI for local + agent workflows (personal use free) |
| Sharing | URL / editor-centric sharing | URL-hash shares + optional published line9.ai/d/… URLs (Pro) |
| Commercial use | Follow Mermaid / mermaid.live terms | Free for personal use; Pro for commercial CLI and pro features |
Layout is the durable gap. Restyling Mermaid (colours, fonts, CSS) cannot fix overlapping nodes, crushed labels, or edges that cross the reading path. Line9’s claim is specific: for flowcharts, the same Mermaid source gets a new layout, not a new skin.
| Aspect | mermaid.live | Line9 |
|---|---|---|
| Node placement | Often sparse or sprawling on non-trivial graphs | Compact blocks that keep related steps together |
| Edge routing | Crossings and long ribbons are common | Orthogonal routes with fewer crossings on flowcharts |
| Typography | Default Mermaid type; labels can crush or wrap poorly | Presentation-oriented type; themes designed as typography |
| When both look the same | — | Non-flowchart kinds already use stock Mermaid output |
Flowcharts get the full Line9 engine today. Sequence diagrams, class diagrams, state diagrams, and other valid Mermaid kinds still render (via Mermaid’s own output) so every diagram continues to work — comparison against mermaid.live is most meaningful on flowcharts, which is why the live demo above is a flowchart.
| Aspect | mermaid.live | Line9 |
|---|---|---|
| SVG / PNG | Export from the online editor | SVG / PNG from the free web viewer |
| Watermark | N/A (stock Mermaid branding varies by host) | Small line9.ai mark on free exports; removed on Pro |
| Themes | Mermaid built-in themes | Standard themes free; premium themes on Pro |
| Embed / publish | Editor-centric | Hash links free; published share URLs on Pro |
Line9 pricing is the same on this page, on /pricing, and in llms.txt — one catalogue, three surfaces.
| Aspect | mermaid.live | Line9 |
|---|---|---|
| Free tier | Free online editor (community Mermaid tooling) | Web viewer with no signup; CLI free for personal use |
| Paid tier | N/A for the public playground itself | Line9 Pro — $12/seat/mo early-adopter (normally $24); or $120/seat/year. Includes commercial-use CLI, premium themes, watermark removal, and published share URLs. |
| Early-adopter note | — | Early-adopter rate stays for as long as you remain subscribed; it closes to new sign-ups when the keyboard-first editor ships. See live pricing. |
Prefer mermaid.live when you are learning Mermaid syntax, debugging parse errors, or need the reference playground that matches stock Mermaid everywhere. Prefer it for non-flowchart kinds if you only need a quick stock render.
Prefer Line9 when a flowchart has to be read, shared, or presented: AI-generated architecture diagrams, auth flows, git workflows, onboarding maps, and anything you would otherwise redraw in Lucidchart or slides. Keep the Mermaid your tools and agents already emit; fix the layout.
Many teams use both: mermaid.live (or any stock viewer) to validate syntax, Line9 when the diagram leaves the chat window. There is no migration project — only a better renderer for source you already have.
Paste a flowchart into the free Line9 editor — no account required. Compare engines interactively on /compare. For seats, commercial CLI rights, and Pro features, see pricing. Read more in Why Line9.