Line9
A Mermaid rendering engine with its own layout
Details
- External ID
- 49196657
- Source
- HN
- Company
- —
- Product
- Line9
- Website domain
- line9.ai
- Launched
- Aug. 6, 2026
- Cohort
- —
- Upvotes
- 87
- Upvotes percentile
- 0.918010752688172
- Tags
- —
- Fetched at
- Sept. 10, 2026, 5:32 a.m.
- Updated at
- Sept. 10, 2026, 5:32 a.m.
Description
Line9 is a new rendering engine for Mermaid flowchart diagrams that aims to remove the need for manual adjustment of layout. Mermaid is a popular text-based language for describing multiple types of diagrams.Several Mermaid rendering engines already exist. Most, like the original mermaid.js, use Dagre or ELK graph drawing libraries to automatically lay out their diagrams. I’ve used Mermaid for the past four years but often recreated my flowcharts in a diagram editor so that I could modify the layout to something that better suited my needs.Use Line9 when you want an automatic flowchart arrangement that optimises for clear communication. It seeks to layout flowcharts with regular grid spacing, closer positioning of related nodes, shorter, straighter edges and targets a page-like aspect ratio. The Compare button in the /diagram page (share panel on the left) shows you the Line9 and mermaid.js renders next to each other.Use for free, no account required. A CLI tool can also be downloaded for Mac, Windows and Linux. Free-use diagrams carry a watermark. Commercial use of the CLI requires a paid account and you also get diagrams without watermarks. Line9 is not open source (I need to create an income and the business model is being tested).I’ve tried to encode and automate the layout principles I use when creating flowcharts by hand. All rendering takes place in the browser, so no private data is sent to the web service. The CLI is written in Rust and embeds the renderer so you get a single binary install and all data and processing remains local. It’s currently a little slower than mermaid.js, due to the difficulty of solving node positioning and edge routing simultaneously to find the layout that best meets the design principles.Output is produced in SVG or PNG formats. Diagrams can also be shared via a URL with a fragment that embeds the Mermaid text.Things I know still need improvement: positioning and rotating subgraphs, folding graphs to hit good aspect ratios more often, further improvement on edge label placement, better interaction with long node labels and tidying up the display when scaling down. Then I also want to support more diagram types and the website needs lots of work.Please paste your own Mermaid flowcharts into Line9 – particularly the ones that you previously discarded because the layout was bad. Let me know whether they improve, or what other work is needed.
Enrichment
- Theme
- 3D graphics and physics simulation tools
- Vertical
- Horizontal
- Function
- Dev tools
- Audience
- Developer
- AI stance
- Not AI
- Project type
- Hobby / open-source project
- Normalized one-liner
- diagram rendering engine
- Manually corrected
- False
Could you build this?
Partial Parsing Mermaid syntax and rendering SVGs is straightforward, but writing a novel automatic graph layout engine that outperforms existing algorithms like Dagre without manual adjustment requires complex algorithmic graph theory.
What it would actually take: Stack involves a parser (likely Lezer or Peggy) targeting Mermaid flowchart syntax and an SVG/Canvas rendering layer (Svelte/TypeScript). The core hard problem is the constraint-satisfaction and graph-layout algorithm (layered graph drawing, Sugiyama-style hierarchical layouts, edge routing without intersections, and port alignment). Developing custom layout engines requires strong background in discrete mathematics, computational geometry, and optimization heuristics.
Discussion
20 comments analyzed.
Competitors mentioned: Mermaid with ELK layout engine, Excalidraw, Lucidchart, Line9 CLI
Concerns raised: Purchasing approval process/budget constraints for individuals, Confluence image caching prevents diagram updates, Need for public visibility to share diagrams via URL, Poor tooling around Mermaid language despite language strengths, Hand-tuning layout parameters still required with alternative engines
Feature requests: Confluence app/plugin for native integration, Handle overlapping edge labels without moving nodes, Support for BPMN diagrams with swimlanes and drill-down levels, Better source-editing and rendering in page experience
Competitors
Other products that read as similar to this one — 80 launches clear the similarity bar, closest 8 shown.
Attention rank: #9 of 81 (itself plus its competitors, highest first — normalized so YC and Product Hunt are compared fairly).
Launched 275 days after the earliest competitor.
- Ferrite · hn · 2026-01-11 · 241 upvotes · similarity 0.63
- Arialine · ph · 2026-09-30 · 1 upvotes · similarity 0.63
- Visimer · hn · 2026-08-17 · 17 upvotes · similarity 0.62
- Mmdr · hn · 2026-02-04 · 47 upvotes · similarity 0.62
- FlowPeek · ph · 2026-09-11 · 2 upvotes · similarity 0.57
- Vloam Mermaid · ph · 2026-09-15 · 1 upvotes · similarity 0.57
- mermaid-element · github · 2026-09-10 · 8 upvotes · similarity 0.54
- Graph2agent; Mermaid diagrams, explained for agents · hn · 2026-08-10 · 7 upvotes · similarity 0.52
Other launches for this product
- No other launches for this product.
Same idea, different domain
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