Mermster
A Native Mermaid Diagram Editor
Write Mermaid syntax in a Monaco editor — the same engine as VS Code. See diagrams render in real time. Export to SVG, PNG, or PDF with full control. No account, no cloud, no tracking.
See it in action
From code to diagram in real time.
Write diagrams as code. See them instantly.
Mermaid diagrams are powerful, but the tools haven't kept up. You're either fighting a browser tab, wrestling with VS Code extensions, or copying between apps. You shouldn't need three tools to write, preview, and export one diagram.
Mermster is a single app that does all three. Write in a real code editor with autocomplete and syntax highlighting, see the diagram update as you type, and export with configurable DPI, padding, and format — all offline, all private.
Everything you need to diagram
Monaco Editor
The same editor engine as VS Code. Mermaid syntax highlighting, autocomplete, error diagnostics, and 10 color themes including Catppuccin, Dracula, and Nord.
Live Preview
See your diagram update as you type. Pan, zoom, minimap. Fullscreen preview mode for presentations.
Full Export Pipeline
SVG, PNG, PDF. Configure DPI, padding, and background color. Save reusable export presets. Quick export with one shortcut.
Command Palette
Everything is searchable and keyboard-accessible. File operations, export, preferences, templates — all from one shortcut.
Diagram Builder
Don't remember the syntax? The builder panel shows context-aware buttons to insert nodes, edges, and styling. Every Mermaid diagram type is supported.
Version History
Automatic snapshots on every save with diff view. Roll back to any previous version. No Git required.
Write in a Real Editor
Mermster uses the same editor engine as VS Code. You get Mermaid syntax highlighting, autocomplete for keywords and node IDs, and real-time error diagnostics — not a textarea with a monospace font.
- Autocomplete for Mermaid keywords and your own node IDs
- Error diagnostics with inline squiggles
- 10 editor themes to match your setup
Export with Control
SVG for scalable graphics. PNG for documentation. PDF for everything else. Set DPI, padding, background color, and save presets so your exports are consistent every time.
- SVG, PNG, and PDF export formats
- Configurable DPI, padding, and backgrounds
- Save and reuse export presets
Built for Accessibility
Four colorblind-safe diagram palettes — deuteranopia, protanopia, tritanopia, and a general-purpose palette. Seven languages. High-contrast themes. Diagrams everyone can read.
- 4 colorblind-safe diagram color palettes
- 7 interface languages
- High-contrast editor themes
Pay once. Use forever.
Everything is free. The only difference is a watermark on exports.
Mermster
Every feature. No account required.
- Full Monaco editor with all 10 themes
- All 12+ Mermaid diagram types
- Live preview with pan, zoom, and minimap
- SVG, PNG, PDF export (with watermark)
- Command palette, diagram builder, outline navigator
- Version history with diff view
- 4 colorblind-safe diagram palettes
- 7 interface languages
Personal
Clean exports. That's the only difference.
- Everything in Free
- Exports without watermark
- Up to 5 devices
- Personal and freelance use
Commercial
For business and team use.
- Everything in Personal
- Up to 10 devices
- Business and commercial use
Mermster is launching soon. Want to be among the first? Join the waitlist and try the beta free in the meantime.
30-day money-back guarantee. Terms of Use · Refund policy
Zero telemetry. Seriously.
Mermster doesn't phone home. No analytics, no usage tracking, no account system. Your diagrams stay on your machine. The only network request is a one-time license activation — and the free tier never needs internet at all.
Frequently asked questions
Is the free tier actually free?
Yes. Every feature works in the free tier. Exports include a small "Made with Mermster" watermark. A $29 license removes it permanently. We never block functionality behind a paywall.
Do I need an internet connection?
Only once, to activate a paid license key. After that, Mermster works fully offline. The free tier never needs internet at all.
Is this a subscription?
No. One-time purchase. No recurring charges. Updates are included.
What diagram types are supported?
Every Mermaid.js diagram type: flowchart, sequence, class, state, entity-relationship, Gantt, pie, mindmap, timeline, user journey, quadrant chart, and git graph.
What file format does Mermster use?
Standard .mmd and .mermaid text files. They're plain text — version them with Git, open them in any editor, share them however you like.
Is my data private?
Mermster has zero telemetry. No analytics, no usage tracking, no account system. Your diagrams stay on your machine. The app never phones home.
What's your refund policy?
30-day money-back guarantee, no questions asked. Email mermster@viaelo.app with your order number and we'll process your refund within 5–10 business days.
How do I get help?
Email mermster@viaelo.app. We typically respond within one business day.
Looking for detailed help? Read the Mermster User Guide.