mermaid-rs-renderer

A fast Mermaid renderer in Rust (flowchart + basic class/state/sequence).

Status

• Supports flowchart / graph with TD/TB/LR/BT/RL and subgraph direction
• Basic classDiagram (class blocks + relations)
• Basic stateDiagram-v2 (states, aliases, transitions, start/end)
• Basic sequenceDiagram (participants, messages, lifelines; no activation or notes yet)
• Node shapes: rectangle, round-rect, stadium, circle/double-circle, diamond, hexagon, cylinder, subroutine, trapezoids, parallelograms
• Edge styles: solid, dotted, thick; arrowheads + circle/cross/diamond decorations; labels
• Styling directives: classDef, class, inline :::class, style (nodes + subgraphs), linkStyle (fill/stroke/text/stroke-width/dasharray + label color)
• Subgraphs (subgraph ... end)
• Mermaid init directives: %%{init}%% (themeVariables subset, JSON5-style allowed)
• Modern default theme

Usage

# Render SVG to stdout
cat diagram.mmd | mmdr -e svg

# Render a Markdown file (all mermaid blocks)
# If output is a directory, renders diagram-1.svg, diagram-2.svg, ...
mmdr -i README.md -o /tmp/diagrams -e svg

# Render to PNG
mmdr -i diagram.mmd -o diagram.png -e png

# Use config file (Mermaid-like themeVariables)
mmdr -i diagram.mmd -o diagram.svg -e svg -c config.json

# Override spacing via CLI
mmdr -i diagram.mmd -o diagram.svg -e svg --nodeSpacing 60 --rankSpacing 120

Install

# From source
cargo install --path .

# From crates.io (once published)
cargo install mermaid-rs-renderer

Homebrew (macOS/Linux):

brew tap 1jehuang/mmdr
brew install mmdr

Scoop (Windows):

scoop bucket add mmdr https://github.com/1jehuang/scoop-mmdr
scoop install mmdr

AUR (Arch):

# Pending publication; PKGBUILD lives at https://github.com/1jehuang/aur-mmdr
# Once published, install via:
yay -S mmdr-bin

Config

We accept a subset of Mermaid themeVariables in a JSON config file. Example:

{
  "themeVariables": {
    "primaryColor": "#F8FAFF",
    "primaryTextColor": "#1C2430",
    "primaryBorderColor": "#C7D2E5",
    "lineColor": "#7A8AA6",
    "secondaryColor": "#F0F4FF",
    "tertiaryColor": "#E8EEFF",
    "edgeLabelBackground": "#FFFFFF",
    "clusterBkg": "#F8FAFF",
    "clusterBorder": "#C7D2E5",
    "background": "#FFFFFF",
    "fontFamily": "Inter, Segoe UI, system-ui",
    "fontSize": 13
  },
  "flowchart": {
    "nodeSpacing": 40,
    "rankSpacing": 80
  }
}

Development

cargo test
cargo run -- -i docs/diagrams/architecture.mmd -o /tmp/arch.svg -e svg

Benchmarks

We include two benchmark layers:

1. Microbenchmarks (parse/layout/render) via Criterion:

cargo bench --bench renderer

2. End-to-end CLI comparison vs Mermaid CLI:

cargo build --release
scripts/bench_compare.py

You can tweak runs with RUNS/WARMUP, or skip mermaid-cli with SKIP_MERMAID_CLI=1.

Latest end-to-end results (January 22, 2026)

Machine: Intel(R) Core(TM) Ultra 7 256V (8 cores), Linux 6.18.2-arch2-1
Node: v25.2.1, mermaid-cli: 11.12.0
Runs: 2 warmup + 8 measured, SVG output

Notes:

• mermaid-cli includes Chromium startup (via Puppeteer), so it has a large fixed cost.
• These are wall-clock timings on this machine; expect different results on your system.

License

MIT