mermaidtui

Deterministic, readable Unicode/ASCII rendering of Mermaid diagrams in your terminal. By Tariq Shams.

Sometimes you need to visualize a diagram in a terminal environment: TUI apps, CI logs or just quick terminal previews, where SVG or heavy headless browsers aren't an option. mermaidtui provides a lightweight engine to render simple Mermaid flowcharts as clean Unicode or ASCII boxes. Written in TypeScript.

Features

• Standard Mermaid Syntax: Supports a subset of the Mermaid flowchart syntax.
• Unicode & ASCII: Beautiful Unicode boxes by default, with an ASCII fallback mode.
• Deterministic Layout: Grid-based layout engine that prioritizes readability.
• Zero Heavy Dependencies: No Mermaid internals, no Chromium/Puppeteer, no SVG conversion.

Supported Syntax (v0.0.5)

Currently v0.0.5 supports a robust subset of flowcharts:

flowchart LR
    A[Start Here] --> B[Process A] --> C[End Goal]
    B --> D[Process B]

• Directions: LR, RL, TB, BT.
• Nodes: Alphanumeric IDs and square labels A[Label with spaces].
• Edges: Directed arrows -->, including Chained Edges (A --> B --> C).
• Visuals: Intelligent corner rendering (┌, ┐, └, ┘) for orthogonal paths.

Showcase

Complex LR Layout

Input:

flowchart LR
    A[Root] --> B[Top Node]
    A --> C[Bottom Node]
    B --> D[Final]
    C --> D

Output:

              ┌────────┐                    
          ┌──▶│Top Node│─────┐              
          │   └────────┘     │              
┌────┐    │                  │     ┌─────┐  
│Root│────┐                  └─┌──▶│Final│  
└────┘    │                    │   └─────┘  
          │                    │            
          │   ┌───────────┐    │            
          └──▶│Bottom Node│────┘            
              └───────────┘                 

Complex TB Layout

Input:

flowchart TB
    A[Root] --> B[Left Node]
    A --> C[Right Node]
    B --> D[Final]
    C --> D

Output:

            ┌────┐               
            │Root│               
            └────┘               
               │                 
               │                 
     ┌─────────└─────────┐       
     ▼                   ▼       
┌─────────┐        ┌──────────┐  
│Left Node│        │Right Node│  
└─────────┘        └──────────┘  
     │                   │       
     │                   │       
     └─────────┌─────────┘       
               ▼                 
            ┌─────┐              
            │Final│              
            └─────┘              

Installation

npm install mermaidtui

Usage

CLI

# Render a file
mermaidtui diagram.mmd

# Pipe input
cat diagram.mmd | mermaidtui --ascii

Library

import { renderMermaidToTui } from 'mermaidtui';

const input = `flowchart LR
    A[Start] --> B[End]`;

const output = renderMermaidToTui(input, { ascii: false });
console.log(output);

Collaborators & Local Development

We welcome contributions! To test changes locally across repositories:

1. Clone & Link:

   git clone https://github.com/tariqshams/mermaidtui.git
   cd mermaidtui
   npm install
   npm run build
   npm link

2. Use in another project:

   cd ../your-other-project
   npm link mermaidtui

3. Run Tests:

   # Run unit tests
   npm test
   
   # View visual output for all test cases
   npm run dump-visual-test

License

Apache 2.0