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Backends

mmdr ships with two Rust rendering engines. Both produce SVG from Mermaid source text. Everything else — PNG, raw pixels, NumPy — is handled by resvg regardless of which backend you choose.

Comparison

merman mermaid-rs-renderer
Default ✅ —
Diagram parity Full (Mermaid @11.15.0) Common types only
Speed Fast Faster
Layout options — theme, node_spacing, rank_spacing, aspect_ratio

Diagram support

Diagram type merman mermaid-rs-renderer
flowchart / graph ✅ ✅
sequenceDiagram ✅ ✅
classDiagram ✅ ✅
stateDiagram ✅ ✅
erDiagram ✅ ✅
pie ✅ ✅
gantt ✅ ✅
timeline ✅ ✅
mindmap ✅ ✅
gitGraph ✅ ✅
xychart ✅ ✅
block diagram ✅ ❌
architecture ✅ ❌
kanban ✅ ❌
c4diagram ✅ ❌
sankey ✅ ❌
packet ✅ ❌

When to use which

Use merman (default) when:

  • You need a diagram type not supported by mermaid-rs-renderer
  • Output correctness and parity with the official library matters
  • You don't need layout fine-tuning

Use mermaid-rs-renderer when:

  • You're rendering simple flowcharts or common diagrams at high volume
  • You want to control layout parameters (node_spacing, aspect_ratio, etc.)
  • Every millisecond counts

Selecting a backend

import mmdr

# merman (default)
d = mmdr.render("flowchart LR; A-->B")

# mermaid-rs-renderer
d = mmdr.render(
    "flowchart LR; A-->B",
    backend="mermaid-rs-renderer",
    theme="classic",
    node_spacing=60.0,
    rank_spacing=80.0,
    aspect_ratio=(16, 9),
)

# merman (default)
mmdr -i diagram.mmd -o output.svg

# mermaid-rs-renderer
mmdr -i diagram.mmd -o output.svg --backend mermaid-rs-renderer --theme classic