merm 0.1.0

Pure Python Mermaid diagram renderer

merm

Pure Python Mermaid diagram renderer. Converts Mermaid markup to SVG with zero JavaScript dependencies.

Install

pip install merm

Usage

Command line

# File to file
merm -i diagram.mmd -o diagram.svg

# Pipe
echo 'graph LR
    A --> B --> C' | merm > diagram.svg

# With uvx (no install needed)
uvx merm -i diagram.mmd -o diagram.svg

Python API

from merm import render_diagram

svg = render_diagram("""
flowchart TD
    A[Start] --> B{Decision}
    B -->|Yes| C[OK]
    B -->|No| D[End]
""")

Supported diagram types

• Flowchart (graph / flowchart) — all directions (TD, LR, BT, RL), subgraphs, shapes, edge labels
• Sequence (sequenceDiagram) — participants, messages, loops, alt/opt/par fragments
• Class (classDiagram) — classes, methods, attributes, relationships
• State (stateDiagram) — states, transitions, composite states, forks/joins

Features

• Pure Python — no Node.js, no browser, no Puppeteer
• Fast — ~200x faster than mermaid-cli (mmdc)
• SVG output with clean markup
• All flowchart shapes and edge types
• Subgraph nesting and styling
• Edge labels and arrow markers

Performance

Benchmarked against mermaid-cli (mmdc) across 28 scenarios:

	merm	mmdc
Average render time	~1 ms	~200 ms
Dependencies	0	Node.js + Puppeteer
Startup overhead	None	~500 ms

License

MIT