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mermaid-rs-renderer

★ 1,650 Open GitHub ↗

A fast native Rust Mermaid diagram renderer. No browser required. 500-1000x faster than mermaid-cli.

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# mmdr

**100–1400x faster Mermaid rendering. Pure Rust. Zero browser dependencies.**

[Installation](#installation) | [Quick Start](#quick-start) | [Benchmarks](#performance) | [Examples](#diagram-types)

</div>

> **Note:** This library is under active early development. Visual output quality is improving rapidly but may not yet match mermaid-cli in all cases. Bug reports and PRs are welcome.

## Performance

mmdr renders diagrams **100–1400x faster** than mermaid-cli by eliminating browser overhead.
With the built-in font cache (warm after first run), tiny diagrams reach **500–900×** (and `--fastText` exceeds **1600×**).

| Diagram | mmdr | mermaid-cli | Speedup |
|:--------|-----:|------------:|--------:|
| Flowchart | 4.49 ms | 1,971 ms | **439x** |
| Class Diagram | 4.67 ms | 1,907 ms | **408x** |
| State Diagram | 3.97 ms | 1,968 ms | **496x** |
| Sequence Diagram | 2.71 ms | 1,906 ms | **704x** |

Tested on Intel Core Ultra 7 265V, Linux 6.18.7 | mermaid-cli 11.4.2 via Puppeteer/Chromium

</div>

<details>
<summary>Font cache (default, warm after first run)</summary>

Once the font cache is populated, tiny/common diagrams reach **500–900×**:

| Diagram (tiny) | mmdr (warm cache) | mermaid-cli | Speedup |
|:--|--:|--:|--:|
| Flowchart | 2.96 ms | 2,259 ms | **764×** |
| Class | 2.55 ms | 2,347 ms | **919×** |
| State | 2.67 ms | 2,111 ms | **789×** |
| Sequence | 3.75 ms | 2,010 ms | **536×** |

Measured Feb 2, 2026 on the same machine.
</details>

<details>
<summary>Fast text metrics (optional, fastest)</summary>

Enable `--fastText` to use calibrated fallback widths for ASCII labels (avoids font DB load).
On tiny/common diagrams this reaches **1600–2069×** speedups:

| Diagram (tiny) | mmdr `--fastText` | mermaid-cli | Speedup |
|:--|--:|--:|--:|
| Flowchart | 1.32 ms | 2,116 ms | **1,601×** |
| Class | 1.23 ms | 2,314 ms | **1,880×** |
| State | 1.09 ms | 2,258 ms | **2,069×** |
| Sequence | 1.16 ms | 2,158 ms | **1,868×** |

Measured Feb 2, 2026 on the same machine.
</details>

<details>
<summary>Library Performance (no CLI overhead)</summary>

When used as a Rust library, mmdr is even faster with no process spawn overhead:

| Diagram | Library Time |
|:--------|-------------:|
| Flowchart | 1.49 ms |
| Class Diagram | 2.51 ms |
| State Diagram | 2.04 ms |
| Sequence Diagram | 0.07 ms |

These are raw render times measured with Criterion, ideal for embedding in applications.

</details>

<details>
<summary>Extended Benchmarks</summary>

Performance on larger diagrams:

| Diagram | Nodes | mmdr | mermaid-cli | Speedup |
|:--------|------:|-----:|------------:|--------:|
| flowchart (small) | 10 | 3.38 ms | 1,910 ms | 565x |
| flowchart (medium) | 50 | 8.71 ms | 2,018 ms | 232x |
| flowchart (large) | 200 | 47.00 ms | 2,276 ms | 48x |

The speedup advantage decreases for very large diagrams as actual layout computation becomes more significant relative to browser startup overhead. The 200-node case above is still **48x faster** in this measurement.

</details>

## Why mmdr?

The official `mermaid-cli` spawns a **headless Chromium browser** for every diagram, adding 2-3 seconds of startup overhead.

| Use Case | mermaid-cli | mmdr |
|:---------|:------------|:-----|
| CI/CD pipeline with 50 diagrams | ~2 minutes | **< 1 second** |
| Real-time editor preview | Unusable lag | **Instant** |
| Batch doc generation | Coffee break | **Blink of an eye** |

mmdr parses Mermaid syntax natively in Rust and renders directly to SVG. No browser. No Node.js. No Puppeteer.

## Installation

```bash
# crates.io (recommended)
cargo install mermaid-rs-renderer

# From source
cargo install --path .

# 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)
yay -S mmdr-bin

# Nix (flake)
nix run github:1jehuang/mermaid-rs-renderer -- --help
nix profile install github:1jehuang/mermaid-rs-renderer
```

## Quick Start

```bash
# Pipe diagram to stdout
echo 'flowchart LR; A-->B-->C' | mmdr -e svg

# Read from stdin, write to a file (use '-i -' for explicit stdin)
echo 'flowchart LR; A-->B-->C' | mmdr -i - -o out.svg -e svg

# File to file
mmdr -i diagram.mmd -o output.svg -e svg
mmdr -i diagram.mmd -o output.png -e png

# Render all diagrams from a Markdown file
mmdr -i README.md -o ./diagrams/ -e svg
```

By default the output uses the diagram's natural dimensions (the root SVG
`width`/`height` match the `viewBox`, so there is no letterbox padding).
Pass `--width`/`--height` to force explicit output dimensions.

## Diagram Types

mmdr supports **23 Mermaid diagram types**:

| Category | Diagrams |
|:---------|:---------|
| **Core** | Flowchart, Sequence, Class, State |
| **Data** | ER Diagram, Pie Chart, XY Chart, Quadrant Chart, Sankey |
| **Planning** | Gantt, Timeline, Journey, Kanban |
| **Architecture** | C4, Block, Architecture, Requirement |
| **Other** | Mindmap, Git Graph, ZenUML, Packet, Radar, Treemap |

<table>
<tr>
<td align="center" width="50%">
Flowchart 
<img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/flowchart_mmdr.svg" alt="Flowchart" width="100%">
</td>
<td align="center" width="50%">
Class Diagram 
<img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/class_mmdr.svg" alt="Class Diagram" width="100%">
</td>
</tr>
<tr>
<td align="center" width="50%">
State Diagram 
<img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/state_mmdr.svg" alt="State Diagram" width="100%">
</td>
<td align="center" width="50%">
Sequence Diagram 
<img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/sequence_mmdr.svg" alt="Sequence Diagram" width="100%">
</td>
</tr>
</table>

<details>
<summary>Compare with mermaid-cli output</summary>

| Type | mmdr | mermaid-cli |
|:-----|:----:|:-----------:|
| Flowchart | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/flowchart_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/flowchart_official.svg" width="350"> |
| Class | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/class_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/class_official.svg" width="350"> |
| State | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/state_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/state_official.svg" width="350"> |
| Sequence | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/sequence_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/sequence_official.svg" width="350"> |
| ER Diagram | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/er_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/er_official.svg" width="350"> |
| Pie Chart | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/pie_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/pie_official.svg" width="350"> |
| Gantt | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/gantt_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/gantt_official.svg" width="350"> |
| Mindmap | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/mindmap_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/mindmap_official.svg" width="350"> |
| Timeline | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/timeline_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/timeline_official.svg" width="350"> |
| Journey | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/journey_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/journey_official.svg" width="350"> |
| Git Graph | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/gitgraph_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/gitgraph_official.svg" width="350"> |
| XY Chart | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/xychart_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/xychart_official.svg" width="350"> |
| Quadrant | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/quadrant_mmdr.svg" width="350"> | <img src="https://raw.githubusercontent.com/1jehuang/mermaid-rs-renderer/master/docs/comparisons/quadrant_official.svg" width="350"> |

</details>

## More Diagrams

<details>
<summary>Node Shapes</summary>

| Shape | Syntax |
|:------|:-------|
| Rectangle | `[text]` |
| Round | `(text)` |
| Stadium | `([text])` |
| Diamond | `{text}` |
| Hexagon | `{{text}}` |
| Cylinder | `[(text)]` |
| Circle | `((text))` |
| Double Circle | `(((text)))` |
| Subroutine | `[[text]]` |
| Parallelogram | `[/text/]` |
| Trapezoid | `[/text\]` |
| Asymmetric | `>text]` |

</details>

<details>
<summary>Edge Styles</summary>

| Type | Syntax | Description |
|:-----|:-------|:------------|
| Arrow | `-->` | Standard arrow |
| Open | `---` | No arrowhead |
| Dotted | `-.->` | Dashed line with arrow |
| Thick | `==>` | Bold arrow |
| Circle end | `--o` | Circle decoration |
| Cross end | `--x` | X decoration |
| Diamond end | `<-->` | Bidirectional |
| With label | `--\|text\|-->` | Labeled edge |

</details>

<details>
<summary>Subgraphs</summary>

```
flowchart TB
    subgraph Frontend
        A[React App] --> B[API Client]
    end
    subgraph Backend
        C[Express Server] --> D[(PostgreSQL)]
    end
    B --> C
```

Subgraphs support:
- Custom labels
- Direction override (`direction LR`)
- Nesting
- Styling

</details>

<details>
<summary>Styling Directives</summary>

```
flowchart LR
    A[Start] --> B[End]

classDef highlight fill:#f9f,stroke:#333
    class A highlight

style B fill:#bbf,stroke:#333
    linkStyle 0 stroke:red,stroke-width:2px
```

Supported:
- `classDef` - Define CSS classes
- `class` - Apply classes to nodes
- `:::class` - Inline class syntax
- `style` - Direct node styling
- `linkStyle` - Edge styling
- `%%{init}%%` - Theme configuration

</details>

## Features

**Node shapes:** rectangle, round-rect, stadium, circle, double-circle, diamond, hexagon, cylinder, subroutine, trapezoid, parallelogram, asymmetric

**Edges:** solid, dotted, thick | Decorations: arrow, circle, cross, diamond | Labels

**Styling:** `classDef`, `class`, `:::class`, `style`, `linkStyle`, `%%{init}%%`

**Layout:** subgraphs with direction, nested subgraphs, automatic spacing

## Configuration

```bash
mmdr -i diagram.mmd -o out.svg -c config.json
mmdr -i diagram.mmd -o out.svg --nodeSpacing 60 --rankSpacing 120
mmdr -i diagram.mmd -o out.svg --preferredAspectRatio 16:9
```

`preferredAspectRatio` is layout-aware for graph diagrams: the renderer first rebalances geometry toward the target ratio, then fits final SVG dimensions to that ratio.

<details>
<summary>config.json example</summary>

```json
{
  "themeVariables": {
    "primaryColor": "#F8FAFF",
    "primaryTextColor": "#1C2430",
    "primaryBorderColor": "#C7D2E5",
    "lineColor": "#7A8AA6",
    "secondaryColor": "#F0F4FF",
    "tertiaryColor": "#E8EEFF",
    "edgeLabelBackground": "#FFFFFF",
    "clusterBkg": "#F8FAFF",
    "clusterBorder": "#C7D2E5",
    "background": "#FFFFFF",
    "fontFamily": "Inter, system-ui, sans-serif",
    "fontSize": 13
  },
  "preferredAspectRatio": "16:9",
  "flowchart": {
    "nodeSpacing": 50,
    "rankSpacing": 50
  }
}
```

</details>

## How It Works

**mmdr** implements the entire Mermaid pipeline natively:

```
.mmd → parser.rs → ir.rs → layout.rs → render.rs → SVG → resvg → PNG
```

**mermaid-cli** requires browser infrastructure:

```
.mmd → mermaid-js → layout → Browser DOM → Puppeteer → Chromium → Screenshot → PNG
```

| | mmdr | mermaid-cli |
|:--|:-----|:------------|
| Runtime | Native binary | Node.js + Chromium |
| Cold start | ~3 ms | ~2,000 ms |
| Memory | ~15 MB | ~300+ MB |
| Dependencies | None | Node.js, npm, Chromium |

## Library Usage

Use mmdr as a Rust library in your project:

```toml
[dependencies]
mermaid-rs-renderer = "0.3.1"
```

<details>
<summary>Minimal dependencies (for embedding)</summary>

For tools like Zola that only need SVG rendering, disable default features to avoid CLI and PNG dependencies:

```toml
[dependencies]
mermaid-rs-renderer = { version = "0.3.1", default-features = false }
```

| Feature | Default | Description |
|:--------|:-------:|:------------|
| `cli` | Yes | CLI binary and clap dependency |
| `png` | Yes | PNG output via resvg/usvg |

With current locked dependencies, this reduces the dependency graph from about 123 crates to about 71 crates.

</details>

For unreleased commits only:

```toml
[dependencies]
mermaid-rs-renderer = { git = "https://github.com/1jehuang/mermaid-rs-renderer", rev = "<commit-sha>" }
```

```rust
use mermaid_rs_renderer::{render, render_with_options, RenderOptions};

// Simple one-liner
let svg = render("flowchart LR; A-->B-->C").unwrap();

// With custom options
let opts = RenderOptions::modern()
    .with_node_spacing(60.0)
    .with_rank_spacing(80.0);
let svg = render_with_options("flowchart TD; X-->Y", opts).unwrap();
```

<details>
<summary>Full pipeline control</summary>

```rust
use mermaid_rs_renderer::{
    parse_mermaid, compute_layout, render_svg,
    Theme, LayoutConfig,
};

let diagram = "flowchart LR; A-->B-->C";

// Stage 1: Parse
let parsed = parse_mermaid(diagram).unwrap();
println!("Parsed {} nodes", parsed.graph.nodes.len());

// Stage 2: Layout
let theme = Theme::modern();
let config = LayoutConfig::default();
let layout = compute_layout(&parsed.graph, &theme, &config);

// Stage 3: Render
let svg = render_svg(&layout, &theme, &config);
```

</details>

<details>
<summary>With timing information</summary>

```rust
use mermaid_rs_renderer::{render_with_timing, RenderOptions};

let result = render_with_timing(
    "flowchart LR; A-->B",
    RenderOptions::default()
).unwrap();

println!("Rendered in {:.2}ms", result.total_ms());
println!("  Parse:  {}us", result.parse_us);
println!("  Layout: {}us", result.layout_us);
println!("  Render: {}us", result.render_us);
```

</details>

## Development

```bash
cargo test
cargo run -- -i docs/diagrams/architecture.mmd -o target/out.svg -e svg
```

**Remote build/test over SSH (optional):**
```bash
scripts/remote-cargo.sh test
scripts/remote-cargo.sh build --release
scripts/remote-cargo.sh bench --bench renderer

# Optional override
MMDR_REMOTE_HOST=my-builder scripts/remote-cargo.sh test
```

The wrapper uses `rsync` + `ssh` and keeps host/IP details in your local environment
or `~/.ssh/config`, not in this repository. By default it syncs into an isolated
directory under remote `~/.cache` with `rsync --delete`, so it will not
touch your normal remote working copy unless you set `MMDR_REMOTE_DIR` to that path.

**Benchmarks:**
```bash
cargo bench --features benchmark --bench renderer  # Microbenchmarks
cargo build --locked --release && python3 scripts/bench_compare.py  # full suite vs mermaid-cli
python3 scripts/bench_render.py --help  # focused end-to-end PNG benchmark options
```

For a faster optimized development build, use `cargo build --profile release-fast`.
The regular release profile keeps fat LTO for published binaries.

Release process: see [docs/release.md](https://github.com/1jehuang/mermaid-rs-renderer/blob/master/docs/release.md).

## License

MIT

mermaid-rs-renderer

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