mmdg (mermaid-go-renderer)

Fast native Mermaid rendering in Go. No browser, no Chromium.

Installation | CLI Usage | Fidelity | Performance | Library Usage | Release and Homebrew

Why this project

mmdg is a pure Go Mermaid renderer for SVG and PNG output.

• Native execution (no browser process)
• Native SVG and PNG output (PNG rasterized in pure Go)
• Usable both as a library and CLI
• Supports Mermaid diagram families through native parsing and rendering
• Focused on low startup latency for local workflows and CI pipelines

Inspiration

This project is inspired by the Rust implementation 1jehuang/mermaid-rs-renderer.

• Original Mermaid CLI: mmdc (@mermaid-js/mermaid-cli)
• Rust renderer: mmdr (mermaid-rs-renderer)
• Go renderer: mmdg (this repository)

Performance

This README includes direct performance and fidelity benchmarking against Mermaid CLI (mmdc).

Benchmark host:

• Apple M4 Max
• macOS darwin 25.1.0
• Go 1.26.0
• Date: 2026-02-26

Fidelity (mmdc-first)

mmdg fidelity is measured against mmdc output as ground truth.

Approach:

1. Render paired outputs for the same fixtures:
   • mmdc -> /tmp/{name}_mmdc.svg
   • mmdg -> /tmp/{name}_mmdg.svg
2. Compute XML deltas (not only visual deltas) with:
   • python3 scripts/svg_xml_delta.py
3. Track three parity gates per fixture:
   • tag_delta
   • attr_presence_delta
   • text_delta
4. Prioritize fixtures with largest structural deltas first.

Reproduce the full fidelity sweep:

./scripts/render_all_components_to_tmp.sh
python3 scripts/svg_xml_delta.py

Latest XML fidelity snapshot (/tmp/svg_xml_delta_report.csv):

• Fixtures compared: 23
• Exact parity (tag_delta=0, attr_presence_delta=0, text_delta=0): 8 / 23
• Structural parity (tag_delta=0, attr_presence_delta=0): 8 / 23

Exact-parity fixtures:

• architecture_complex, block_complex, gantt_complex, mindmap_complex
• radar_complex, sankey_complex, sequence_complex, treemap_complex

Current highest-delta fixtures (XML-first backlog):

• flowchart_complex (tag=55, attr=272, text=5)
• gitgraph_complex (tag=24, attr=268, text=2)
• c4_context_complex (tag=47, attr=181, text=23)
• requirement_complex (tag=73, attr=149, text=18)

Method:

• warm-up pass for each tool and fixture
• repeated CLI runs (mmdg: 20, mmdr: 20, mmdc: 5)
• measured wall-clock render command time

Renderer stack comparison

Tool	Role	Implementation	Runtime stack
mmdc	Original Mermaid CLI	JavaScript	Node.js + Puppeteer + headless Chromium
mmdr	Rust version	Rust	Native binary
mmdg	Our version	Go	Native binary

CLI render benchmark (mmdc vs mmdr vs mmdg)

Diagram	mmdc avg	mmdr avg	mmdg avg	mmdr vs mmdc	mmdg vs mmdc
Flowchart	2450.55 ms	18.85 ms	13.94 ms	129.99x	175.78x
Sequence	2356.64 ms	32.60 ms	15.56 ms	72.30x	151.46x
Class	2594.45 ms	18.47 ms	15.76 ms	140.47x	164.61x
State	2623.20 ms	20.41 ms	18.18 ms	128.51x	144.27x

Geometric mean speedup vs mmdc:

• mmdr (Rust): 114.13x
• mmdg (Go): 158.58x

On this run, mmdg is faster than mmdr on these representative fixtures.

Library microbenchmarks (go test -bench)

Benchmark	Time	Memory	Allocs
Flowchart	121,343 ns/op	44,314 B/op	418
Sequence	54,838 ns/op	46,253 B/op	206
State	158,538 ns/op	62,489 B/op	302
Class	70,093 ns/op	59,870 B/op	249
Pie	96,986 ns/op	50,901 B/op	390
XY Chart	104,718 ns/op	67,371 B/op	535

Reproduce library benchmarks:

go test -run ^$ -bench BenchmarkRender -benchmem ./...

Installation

Homebrew (recommended)

brew tap bvolpato/tap
brew install bvolpato/tap/mmdg
mmdg --help

Upgrade later:

brew update
brew upgrade mmdg

Download prebuilt binary (GitHub Releases)

Pick the archive for your OS/arch from:

• https://codeberg.org/hum3/mermaid-go-renderer/releases/latest

Example (darwin_arm64):

VERSION="v0.2.0" # replace with the version you want
curl -L "https://codeberg.org/hum3/mermaid-go-renderer/releases/download/${VERSION}/mermaid-go-renderer_${VERSION#v}_darwin_arm64.tar.gz" -o mmdg.tar.gz
tar -xzf mmdg.tar.gz
chmod +x mmdg
sudo mv mmdg /usr/local/bin/mmdg
mmdg --help

If you have multiple mmdg binaries in PATH, check with:

which -a mmdg

Build locally

git clone https://codeberg.org/hum3/mermaid-go-renderer
cd mermaid-go-renderer
go build ./cmd/mmdg

Install with go install

go install codeberg.org/hum3/mermaid-go-renderer/cmd/mmdg@latest

CLI Usage

Render a Mermaid file to SVG:

mmdg -i diagram.mmd -o out.svg -e svg

Render a Mermaid file to PNG:

mmdg -i diagram.mmd -o out.png -e png

Render from stdin:

echo 'flowchart LR; A-->B-->C' | mmdg -e svg

Render all Mermaid blocks from Markdown:

mmdg -i docs.md -o ./out -e svg

Useful flags:

• --nodeSpacing
• --rankSpacing
• --preferredAspectRatio (16:9, 4/3, 1.6)
• --fastText
• --timing

Diagram support

Current parser and renderer paths detect and handle Mermaid families including:

• Flowchart, Sequence, Class, State, ER, Pie
• Mindmap, Journey, Timeline, Gantt, Git Graph
• XY Chart, Quadrant
• Requirement, C4, Sankey, ZenUML, Block, Packet, Kanban, Architecture, Radar, Treemap

Library Usage

Add the dependency:

go get codeberg.org/hum3/mermaid-go-renderer@latest

Simple API:

package main

import (
	"fmt"

	mermaid "codeberg.org/hum3/mermaid-go-renderer"
)

func main() {
	svg, err := mermaid.Render("flowchart LR\nA[Start] --> B{Decision}\nB --> C[Done]")
	if err != nil {
		panic(err)
	}
	fmt.Println(svg)
}

Write PNG directly from Go:

package main

import (
	mermaid "codeberg.org/hum3/mermaid-go-renderer"
)

func main() {
	svg, err := mermaid.RenderWithOptions("flowchart LR\nA-->B", mermaid.DefaultRenderOptions())
	if err != nil {
		panic(err)
	}
	if err := mermaid.WriteOutputPNG(svg, "out.png"); err != nil {
		panic(err)
	}
}

Pipeline API:

parsed, _ := mermaid.ParseMermaid("flowchart LR\nA-->B")
layout := mermaid.ComputeLayout(&parsed.Graph, mermaid.ModernTheme(), mermaid.DefaultLayoutConfig())
svg := mermaid.RenderSVG(layout, mermaid.ModernTheme(), mermaid.DefaultLayoutConfig())

Architecture

Native rendering pipeline:

.mmd -> parser -> IR graph -> layout -> SVG renderer

No browser process is spawned.

Testing

go test ./...
go test -race ./...
go vet ./...
go build ./...

Release and Homebrew

GoReleaser and CI are configured:

• .goreleaser.yaml (schema version 2)
• .github/workflows/ci.yml
• .github/workflows/release.yml

Release workflow on tag (v*) does:

• cross-platform binary builds
• archives + checksums
• GitHub Release publishing
• Homebrew formula updates in bvolpato/homebrew-tap

Required GitHub secret:

• HOMEBREW_TAP_GITHUB_TOKEN (token with write access to the tap repository)

Links

Documentation	https://h3-mermaid-go-renderer.statichost.page/
Source (Codeberg)	https://codeberg.org/hum3/mermaid-go-renderer
Mirror (GitHub)	https://github.com/drummonds/mermaid-go-renderer