Beautiful Mermaid Diagram Rendering

Render Mermaid diagrams as SVG and PNG images using the Beautiful Mermaid library.

Philosophy

Favor deterministic, high-quality renders over quick hacks.
Keep the workflow minimal and reproducible.
Never auto-install dependencies without explicit approval.

When to use

The user provides Mermaid code and wants SVG/PNG outputs.
The user describes a diagram and wants it rendered as Mermaid images.
The user needs high-resolution diagram assets for docs or slides.

Inputs

Mermaid code (string) or a path to a .mmd file.
Output base name (without extension).
Theme selection (optional; default default).
Whether PNG capture is required (default: yes).

Outputs

<output>.svg (vector output).
<output>.png (high-resolution screenshot) when PNG capture is requested.
Notes on theme and any constraints applied.

Constraints / Safety

Redact or avoid sensitive data in diagram content by default.
Do not auto-install dependencies unless explicitly approved (--allow-install).
Prefer installed runtimes/tools; avoid npx downloads without approval.
Use local file paths for agent-browser; do not open remote URLs.
Only remove intermediary files with explicit confirmation.

Validation

Verify SVG exists and is non-empty.
If PNG capture is requested, confirm the PNG exists and is readable.
Fail fast on missing inputs or unsupported themes.

Anti-patterns

Rendering diagrams that include secrets or tokens.
Running install commands without approval.
Capturing screenshots of remote pages or sensitive content.
Deleting files without confirmation.

Examples

"Render this Mermaid sequence diagram to SVG and PNG."
"Create a flowchart diagram image from this description."
"Use the tokyo-night theme and output to onboarding-diagram."

Dependencies

This skill requires the agent-browser skill for PNG rendering. Load it before proceeding with PNG capture.

Runtime notes:

Prefer runtimes/tools that are already installed (bun, tsx, deno).
Avoid auto-installing dependencies unless explicitly approved.

Supported Diagram Types

Flowchart - Process flows, decision trees, CI/CD pipelines
Sequence - API calls, OAuth flows, database transactions
State - State machines, connection lifecycles
Class - UML class diagrams, design patterns
Entity-Relationship - Database schemas, data models

Available Themes

Default, Dracula, Solarized, Zinc Dark, Tokyo Night, Tokyo Night Storm, Tokyo Night Light, Catppuccin Latte, Nord, Nord Light, GitHub Dark, GitHub Light, One Dark.

If no theme is specified, use default.

Common Syntax Patterns

Flowchart Edge Labels

Use pipe syntax for edge labels:

A -->|label| B
A ---|label| B

Avoid space-dash syntax which can cause incomplete renders:

A -- label --> B   # May cause issues

Node Labels with Special Characters

Wrap labels containing special characters in quotes:

A["Label with (parens)"]
B["Label with / slash"]

Workflow

Step 1: Generate or Validate Mermaid Code

If the user provides a description rather than code, generate valid Mermaid syntax. Consult references/mermaid-syntax.md for full syntax details.

Step 2: Render SVG

Run the rendering script to produce an SVG file:

bun run scripts/render.ts --code "graph TD; A-->B" --output diagram --theme default

Or from a file:

bun run scripts/render.ts --input diagram.mmd --output diagram --theme tokyo-night

Alternative runtimes:

npx tsx scripts/render.ts --code "..." --output diagram
deno run --allow-read --allow-write --allow-net scripts/render.ts --code "..." --output diagram

If dependencies are missing, install them explicitly or re-run with --allow-install:

bun run scripts/render.ts --code "..." --output diagram --allow-install

This produces <output>.svg in the current working directory.

Step 3: Create HTML Wrapper

Run the HTML wrapper script to prepare for screenshot:

bun run scripts/create-html.ts --svg diagram.svg --output diagram.html

This creates a minimal HTML file that displays the SVG with proper padding and background.

Step 4: Capture High-Resolution PNG with agent-browser

Use the agent-browser CLI to capture a high-quality screenshot. Refer to the agent-browser skill for full CLI documentation.

# Set 4K viewport for high-resolution capture
agent-browser set viewport 3840 2160

# Open the HTML wrapper
agent-browser open "file://$(pwd)/diagram.html"

# Wait for render to complete
agent-browser wait 1000

# Capture full-page screenshot
agent-browser screenshot --full diagram.png

# Close browser
agent-browser close

For even higher resolution on complex diagrams, increase the viewport further or use the --padding option when creating the HTML wrapper to give the diagram more space.

Step 5: Clean Up Intermediary Files

After rendering, remove all intermediary files. Only the final .svg and .png should remain.

Files to clean up:

The HTML wrapper file (e.g., diagram.html)
Any temporary .mmd files created to hold diagram code
Any other files created during the rendering process

rm diagram.html

If a temporary .mmd file was created, remove it as well.

Output files (details)

By default, both outputs are produced:

SVG: Vector format, infinitely scalable, small file size.
PNG: High-resolution raster captured at 4K (3840×2160) viewport with minimum 1200px diagram width.

Files are saved to the current working directory unless the user explicitly specifies a different path.

Theme Selection Guide

Theme	Background	Best For
default	Light grey	General use
dracula	Dark purple	Dark mode preference
tokyo-night	Dark blue	Modern dark aesthetic
tokyo-night-storm	Darker blue	Higher contrast
nord	Dark arctic	Muted, calm visuals
nord-light	Light arctic	Light mode with soft tones
github-dark	GitHub dark	Matches GitHub UI
github-light	GitHub light	Matches GitHub UI
catppuccin-latte	Warm light	Soft pastel aesthetic
solarized	Tan/cream	Solarized colour scheme
one-dark	Atom dark	Atom editor aesthetic
zinc-dark	Neutral dark	Minimal, no colour bias

Troubleshooting

Theme not applied

Check the render script output for the bg and fg values, or inspect the SVG's opening tag for --bg and --fg CSS custom properties.

Diagram appears cut off or incomplete

Check edge label syntax — use -->|label| pipe notation, not -- label -->
Verify all node IDs are unique
Check for unclosed brackets in node labels

Render produces empty or malformed SVG

Validate Mermaid syntax at https://mermaid.live before rendering
Check for special characters that need escaping (wrap in quotes)
Ensure flowchart direction is specified (graph TD, graph LR, etc.)

beautiful-mermaid