GitHub - lukilabs/beautiful-mermaid

beautiful-mermaid

Render Mermaid diagrams as beautiful SVGs or ASCII art

Ultra-fast, fully themeable, zero DOM dependencies. Built for the AI era.

Live Demo & Samples

→ Use it live in Craft Agents

Why We Built This

Diagrams are essential for AI-assisted programming. When you're working with an AI coding assistant, being able to visualize data flows, state machines, and system architecture—directly in your terminal or chat interface—makes complex concepts instantly graspable.

Mermaid is the de facto standard for text-based diagrams. It's brilliant. But the default renderer has problems:

• Aesthetics — Might be personal preference, but wished they looked more professional

• Complex theming — Customizing colors requires wrestling with CSS classes

• No terminal output — Can't render to ASCII for CLI tools

• Heavy dependencies — Pulls in a lot of code for simple diagrams

We built beautiful-mermaid at Craft to power diagrams in Craft Agents . It's fast, beautiful, and works everywhere—from rich UIs to plain terminals.

The ASCII rendering engine is based on mermaid-ascii by Alexander Grooff. We ported it from Go to TypeScript and extended it. Thank you Alexander for the excellent foundation! (And inspiration that this was possible.)

Features

• 6 diagram types — Flowcharts, State, Sequence, Class, ER, and XY Charts (bar, line, combined)

• Dual output — SVG for rich UIs, ASCII/Unicode for terminals

• Synchronous rendering — No async, no flash. Works with React useMemo()

• 15 built-in themes — And dead simple to add your own

• Full Shiki compatibility — Use any VS Code theme directly

• Live theme switching — CSS custom properties, no re-render needed

• Mono mode — Beautiful diagrams from just 2 colors

• Zero DOM dependencies — Pure TypeScript, works everywhere

• Ultra-fast — Renders 100+ diagrams in under 500ms

Installation

npm install beautiful-mermaid

or

bun add beautiful-mermaid

or

pnpm add beautiful-mermaid

Quick Start

SVG Output

import { renderMermaidSVG } from 'beautiful-mermaid'

const svg = renderMermaidSVG ( graph TD A[Start] --> B{Decision} B -->|Yes| C[Action] B -->|No| D[End] )

Rendering is fully synchronous — no await , no promises. The ELK.js layout engine runs synchronously via a FakeWorker bypass, so you get your SVG string instantly.

Need async? Use renderMermaidSVGAsync() — same output, returns a Promise<string> .

ASCII Output

import { renderMermaidASCII } from 'beautiful-mermaid'

const ascii = renderMermaidASCII ( graph LR; A --> B --> C )

┌───┐ ┌───┐ ┌───┐ │ │ │ │ │ │ │ A │────►│ B │────►│ C │ │ │ │ │ │ │ └───┘ └───┘ └───┘

React Integration

Because rendering is synchronous, you can use useMemo() for zero-flash diagram rendering:

import { renderMermaidSVG } from 'beautiful-mermaid'

function MermaidDiagram ( { code } : { code : string } ) { const { svg , error } = React .

useMemo ( ( ) => { try { return { svg : renderMermaidSVG ( code , { bg : 'var(--background)' , fg : 'var(--foreground)' , transparent : true , } ) , error : null , } } catch ( err ) { return { svg : null , error : err instanceof Error ?

err : new Error ( String ( err ) ) } } } , [ code ] )

if ( error ) return < pre > { error . message } </ pre > return < div dangerouslySetInnerHTML = { { __html : svg ! } } /> }

Why this works well:

• No flash — SVG is computed synchronously during render, not in a useEffect

• CSS variables — Pass var(--background) etc. instead of hex colors. The SVG inherits from your app's CSS, so theme switches apply instantly without re-rendering

• Memoized — Only re-renders when code changes

Theming

The theming system is the heart of beautiful-mermaid . It's designed to be both powerful and dead simple.

The Two-Color Foundation

Every diagram needs just two colors: background ( bg ) and foreground ( fg ). That's it. From these two colors, the entire diagram is derived using color-mix() :

const svg = renderMermaidSVG ( diagram , { bg : '#1a1b26' , // Background fg : '#a9b1d6' , // Foreground } )

This is Mono Mode —a coherent, beautiful diagram from just two colors. The system automatically derives:

Element Derivation

Text --fg at 100%

Secondary text --fg at 60% into --bg

Edge labels --fg at 40% into --bg

Faint text --fg at 25% into --bg

Connectors --fg at 50% into --bg

Arrow heads --fg at 85% into --bg

Node fill --fg at 3% into --bg

Group header --fg at 5% into --bg

Inner strokes --fg at 12% into --bg

Node stroke --fg at 20% into --bg

Enriched Mode

For richer themes, you can provide optional "enrichment" colors that override specific derivations:

const svg = renderMermaidSVG ( diagram , { bg : '#1a1b26' , fg : '#a9b1d6' , // Optional enrichment: line : '#3d59a1' , // Edge/connector color accent : '#7aa2f7' , // Arrow heads, highlights muted : '#565f89' , // Secondary text, labels surface : '#292e42' , // Node fill tint border : '#3d59a1' , // Node stroke } )

If an enrichment color isn't provided, it falls back to the color-mix() derivation. This means you can provide just the colors you care about.

CSS Custom Properties = Live Switching

All colors are CSS custom properties on the <svg> element. This means you can switch themes instantly without re-rendering:

// Switch theme by updating CSS variables svg . style . setProperty ( '--bg' , '#282a36' ) svg . style . setProperty ( '--fg' , '#f8f8f2' ) // The entire diagram updates immediately

For React apps, pass CSS variable references instead of hex values:

const svg = renderMermaidSVG ( diagram , { bg : 'var(--background)' , fg : 'var(--foreground)' , accent : 'var(--accent)' , transparent : true , } ) // Theme switches apply automatically via CSS cascade — no re-render needed

Built-in Themes

15 carefully curated themes ship out of the box:

Theme Type Background Accent

zinc-light Light #FFFFFF Derived

zinc-dark Dark #18181B Derived

tokyo-night Dark #1a1b26 #7aa2f7

tokyo-night-storm Dark #24283b #7aa2f7

tokyo-night-light Light #d5d6db #34548a

catppuccin-mocha Dark #1e1e2e #cba6f7

catppuccin-latte Light #eff1f5 #8839ef

nord Dark #2e3440 #88c0d0

nord-light Light #eceff4 #5e81ac

dracula Dark #282a36 #bd93f9

github-light Light #ffffff #0969da

github-dark Dark #0d1117 #4493f8

solarized-light Light #fdf6e3 #268bd2

solarized-dark Dark #002b36 #268bd2

one-dark Dark #282c34 #c678dd

import { renderMermaidSVG , THEMES } from 'beautiful-mermaid'

const svg = renderMermaidSVG ( diagram , THEMES [ 'tokyo-night' ] )

Adding Your Own Theme

Creating a theme is trivial. At minimum, just provide bg and fg :

const myTheme = { bg : '#0f0f0f' , fg : '#e0e0e0' , }

const svg = renderMermaidSVG ( diagram , myTheme )

Want richer colors? Add any of the optional enrichments:

const myRichTheme = { bg : '#0f0f0f' , fg : '#e0e0e0' , accent : '#ff6b6b' , // Pop of color for arrows muted : '#666666' , // Subdued labels }

Full Shiki Compatibility

Use any VS Code theme directly via Shiki integration. This gives you access to hundreds of community themes:

import { getSingletonHighlighter } from 'shiki' import { renderMermaidSVG , fromShikiTheme } from 'beautiful-mermaid'

// Load any theme from Shiki's registry const highlighter = await getSingletonHighlighter ( { themes : [ 'vitesse-dark' , 'rose-pine' , 'material-theme-darker' ] } )

// Extract diagram colors from the theme const colors = fromShikiTheme ( highlighter . getTheme ( 'vitesse-dark' ) )

const svg = renderMermaidSVG ( diagram , colors )

The fromShikiTheme() function intelligently maps VS Code editor colors to diagram roles:

Editor Color Diagram Role

editor.background bg

editor.foreground fg

editorLineNumber.foreground line

focusBorder / keyword token accent

comment token muted

editor.selectionBackground surface

editorWidget.border border

Supported Diagrams

Flowcharts

graph TD A[Start] --> B{Decision} B -->|Yes| C[Process] B -->|No| D[End] C --> D

All directions supported: TD (top-down), LR (left-right), BT (bottom-top), RL (right-left).

State Diagrams

stateDiagram-v2 [*] --> Idle Idle --> Processing: start Processing --> Complete: done Complete --> [*]

Sequence Diagrams

sequenceDiagram Alice->>Bob: Hello Bob! Bob-->>Alice: Hi Alice! Alice->>Bob: How are you? Bob-->>Alice: Great, thanks!

Class Diagrams

classDiagram Animal <|-- Duck Animal <|-- Fish Animal: +int age Animal: +String gender Animal: +isMammal() bool Duck: +String beakColor Duck: +swim() Duck: +quack()

ER Diagrams

erDiagram CUSTOMER ||--o{ ORDER : places ORDER ||--|{ LINE_ITEM : contains PRODUCT ||--o{ LINE_ITEM : "is in"

Inline Edge Styling

Use linkStyle to override edge colors and stroke widths — just like Mermaid's linkStyle :

graph TD A --> B --> C linkStyle 0 stroke:#ff0000,stroke-width:2px linkStyle default stroke:#888888

Syntax Effect

linkStyle 0 stroke:#f00 Style a single edge by index (0-based)

linkStyle 0,2 stroke:#f00 Style multiple edges at once

linkStyle default stroke:#888 Default style applied to all edges

Index-specific styles override the default. Supported properties: stroke , stroke-width .

Works in both flowcharts and state diagrams.

XY Charts

Bar charts, line charts, and combinations — using Mermaid's xychart-beta syntax.

Bar chart:

xychart-beta title "Monthly Revenue" x-axis [Jan, Feb, Mar, Apr, May, Jun] y-axis "Revenue ($K)" 0 --> 500 bar [180, 250, 310, 280, 350, 420]

Line chart:

xychart-beta title "User Growth" x-axis [Jan, Feb, Mar, Apr, May, Jun] line [1200, 1800, 2500, 3100, 3800, 4500]

Combined bar + line:

xychart-beta title "Sales with Trend" x-axis [Jan, Feb, Mar, Apr, May, Jun] bar [300, 380, 280, 450, 350, 520] line [300, 330, 320, 353, 352, 395]

Horizontal orientation:

xychart-beta horizontal title "Language Popularity" x-axis [Python, JavaScript, Java, Go, Rust] bar [30, 25, 20, 12, 8]

Axis configuration:

• Categorical x-axis: x-axis [A, B, C]

• Numeric x-axis range: x-axis 0 --> 100

• Axis titles: x-axis "Category" [A, B, C]

• Y-axis range: y-axis "Score" 0 --> 100

Multi-series: Add multiple bar and/or line declarations. Each series gets a distinct color from a monochromatic palette derived from the theme's accent color.

XY Chart Styling

The chart renderer follows a clean, minimal design philosophy inspired by Apple and Craft:

• Dot grid — A subtle dot pattern fills the plot area instead of traditional solid grid lines

• Rounded bars — All bar corners are rounded for a modern, polished look

• Smooth curves — Line series use natural cubic spline interpolation, producing mathematically smooth curves through all data points (not straight segments or staircase steps)

• Floating labels — No visible axis lines or tick marks; labels float freely for a clutter-free aesthetic

• Drop-shadow lines — Each line series has a subtle shadow beneath it for depth

• Monochromatic palette — Series 0 uses the theme's accent color; additional series get darker/lighter shades of the same hue with subtle hue drift, adapting automatically to light or dark backgrounds

• Interactive tooltips — When rendered with interactive: true , hovering over bars or data points shows value tooltips. Multi-line tooltips appear when multiple series share an x-position

• Sparse line dots — Lines with 12 or fewer data points show data point dots by default for readability

• Full theme support — All 15 built-in themes (and custom themes) apply to charts. The accent color drives the entire series color palette

• Live theme switching — Chart series colors are CSS custom properties ( --xychart-color-N ), so theme changes apply instantly without re-rendering

ASCII Output

For terminal environments, CLI tools, or anywhere you need plain text, render to ASCII or Unicode box-drawing characters:

import { renderMermaidASCII } from 'beautiful-mermaid'

// Unicode mode (default) — prettier box drawing const unicode = renderMermaidASCII ( graph LR; A --> B )

// Pure ASCII mode — maximum compatibility const ascii = renderMermaidASCII ( graph LR; A --> B , { useAscii : true } )

Unicode output:

┌───┐ ┌───┐ │ │ │ │ │ A │────►│ B │ │ │ │ │ └───┘ └───┘

ASCII output:

+---+ +---+ | | | | | A |---->| B | | | | | +---+ +---+

ASCII Options

renderMermaidASCII ( diagram , { useAscii : false , // true = ASCII, false = Unicode (default) paddingX : 5 , // Horizontal spacing between nodes paddingY : 5 , // Vertical spacing between nodes boxBorderPadding : 1 , // Padding inside node boxes colorMode : 'auto' , // 'none' | 'auto' | 'ansi16' | 'ansi256' | 'truecolor' | 'html' theme : { .

} , // Partial<AsciiTheme> — override default colors } )

ASCII XY Charts

XY charts render to ASCII with dedicated chart-drawing characters:

• Bar charts — █ blocks (Unicode) or # (ASCII mode)

• Line charts — Staircase routing with rounded corners: ╭╮╰╯│─ (Unicode) or +|- (ASCII)

• Multi-series — Each series gets a distinct ANSI color from the theme's accent palette

• Legends — Automatically shown when multiple series are present

• Horizontal charts — Fully supported with categories on the y-axis

API Reference

renderMermaidSVG(text, options?): string

Render a Mermaid diagram to SVG. Synchronous. Auto-detects diagram type.

Parameters:

• text — Mermaid source code

• options — Optional RenderOptions object

RenderOptions:

Option Type Default Description

bg string #FFFFFF Background color (or CSS variable)

fg string #27272A Foreground color (or CSS variable)

line string? — Edge/connector color

accent string? — Arrow heads, highlights

muted string? — Secondary text, labels

surface string? — Node fill tint

border string? — Node stroke color

font string Inter Font family

transparent boolean false Render with transparent background

padding number 40 Canvas padding in px

nodeSpacing number 24 Horizontal spacing between sibling nodes

layerSpacing number 40 Vertical spacing between layers

componentSpacing number 24 Spacing between disconnected components

thoroughness number 3 Crossing minimization trials (1-7, higher = better but slower)

interactive boolean false Enable hover tooltips on XY chart bars and data points

XY Charts: Diagrams starting with xychart-beta are auto-detected — no separate function needed. The accent color option drives the chart series color palette.

renderMermaidSVGAsync(text, options?): Promise<string>

Async version of renderMermaidSVG() . Same output, returns a Promise<string> . Useful in async server handlers or data loaders.

renderMermaidASCII(text, options?): string

Render a Mermaid diagram to ASCII/Unicode text. Synchronous.

AsciiRenderOptions:

Option Type Default Description

useAscii boolean false Use ASCII instead of Unicode

paddingX number 5 Horizontal node spacing

paddingY number 5 Vertical node spacing

boxBorderPadding number 1 Inner box padding

colorMode string 'auto' 'none' , 'auto' , 'ansi16' , 'ansi256' , 'truecolor' , or 'html'

theme Partial<AsciiTheme> — Override default colors for ASCII output

parseMermaid(text): MermaidGraph

Parse Mermaid source into a structured graph object (for custom processing).

fromShikiTheme(theme): DiagramColors

Extract diagram colors from a Shiki theme object.

THEMES: Record<string, DiagramColors>

Object containing all 15 built-in themes.

DEFAULTS: { bg: string, fg: string }

Default colors ( #FFFFFF / #27272A ).

Attribution

The ASCII rendering engine is based on mermaid-ascii by Alexander Grooff. We ported it from Go to TypeScript and extended it with:

• Sequence diagram support

• Class diagram support

• ER diagram support

• Unicode box-drawing characters

• Configurable spacing and padding

Thank you Alexander for the excellent foundation!

License

MIT — see LICENSE for details.

Built with care by the team at Craft

— 本文由 AI 根据公开来源辅助整理，命令、版本与许可证请在使用前到原始页面复核。