ComfyUI Kroki Wrapper

A ComfyUI custom node for rendering diagrams using the Kroki API. Create beautiful diagrams from text descriptions directly in your ComfyUI workflows.

Features

• 22+ Diagram Types: Mermaid, PlantUML, GraphViz, D2, Excalidraw, and many more
• High-Quality Scaling: Uses ImageMagick to convert vector SVG to any resolution without quality loss
• Customizable Output: Control width, height, and background color
• Self-Hosting Support: Use the public Kroki service or point to your own instance
• ComfyUI Native: Outputs standard image tensors compatible with all ComfyUI nodes

Installation

1. Clone or download this repository into your ComfyUI custom_nodes folder:

   cd ComfyUI/custom_nodes
   git clone https://github.com/yourusername/comfyui-kroki-wrapper.git

2. Restart ComfyUI

The node will appear under image/generation → Render Diagram (Kroki)

Requirements

This node requires Playwright (headless browser) for high-quality SVG to PNG conversion with full foreignObject support.

Installing Playwright

Playwright will be auto-installed when you first load the node in ComfyUI. However, you can also install it manually:

pip install playwright
playwright install chromium

Note: The Chromium browser binary download is approximately 300MB. This is a one-time download.

Why Playwright?

Many modern diagram types (especially Mermaid) use SVG foreignObject elements that contain HTML/CSS. These require a full browser rendering engine to display correctly. Playwright provides this capability with excellent reliability across all diagram types.

Python Dependencies

• playwright (auto-installed by the node)
• requests (usually already included with ComfyUI)
• Pillow (usually already included with ComfyUI)

Usage

Basic Example - Mermaid Diagram

1. Add the "Render Diagram (Kroki)" node to your workflow
2. Set diagram_type to mermaid
3. Enter your Mermaid code in diagram_code:

   graph TD
       A[Start] --> B{Decision}
       B -->|Yes| C[Action 1]
       B -->|No| D[Action 2]
       C --> E[End]
       D --> E
   

4. Adjust width/height as needed
5. Connect the output to other ComfyUI image nodes

Supported Diagram Types

• mermaid - Flowcharts, sequence diagrams, Gantt charts
• plantuml - UML diagrams, wireframes
• graphviz - DOT language graphs
• d2 - Modern declarative diagramming language
• excalidraw - Hand-drawn style diagrams
• blockdiag - Simple block diagrams
• seqdiag - Sequence diagrams
• dbml - Database diagrams
• erd - Entity relationship diagrams
• nomnoml - UML diagrams
• wavedrom - Digital timing diagrams
• And many more!

See Kroki documentation for full list and syntax examples.

Parameters

Parameter	Description	Default
diagram_code	Your diagram code (syntax depends on diagram type)	Mermaid example
diagram_type	Type of diagram to render	mermaid
width	Output image width in pixels	1024
height	Output image height in pixels	768
background_color	Background color (transparent/white/black/custom)	white
custom_bg_color	Custom hex color (when background_color = custom)	#ffffff
kroki_url	Kroki service URL (for self-hosting)	https://kroki.io

Example Workflows

PlantUML Class Diagram:

@startuml
class User {
  +String name
  +String email
  +login()
}
class Admin {
  +String role
  +deleteUser()
}
User <|-- Admin
@enduml

GraphViz Network Diagram:

digraph G {
  rankdir=LR;
  node [shape=circle];
  A -> B -> C;
  A -> C;
}

Self-Hosting

For offline use or privacy, you can run your own Kroki instance:

docker run -d -p 8000:8000 yuzutech/kroki

Then set kroki_url to http://localhost:8000 in the node.

How It Works

1. Your diagram code is compressed (deflate) and base64-encoded
2. Sent to Kroki API via HTTP GET request
3. Kroki renders the diagram as vector SVG
4. Playwright (headless Chromium) renders the SVG in a browser context at your specified resolution
5. Screenshot is captured as PNG with perfect quality and full HTML/CSS support
6. Result is converted to ComfyUI image tensor for use in your workflow

This approach ensures diagrams remain sharp and crisp at any resolution, with full support for modern diagram features like foreignObject elements!

Privacy & Internet Connection

• Public service: Sends your diagram code to https://kroki.io (requires internet)
• Self-hosted: No data leaves your machine (works offline)

The Kroki project is open-source and privacy-respecting.

Troubleshooting

"Failed to render SVG using Playwright"

• Make sure Playwright and Chromium are installed: pip install playwright && playwright install chromium
• Check that you have enough disk space (~300MB for Chromium)
• On some systems, you may need to install additional dependencies for Chromium to run

"Failed to render diagram via Kroki"

• Check your internet connection
• Verify the diagram code syntax is correct for the selected diagram type
• Try the example code for that diagram type from Kroki docs

Node doesn't appear in ComfyUI

• Ensure the file is named __init__.py in the custom_nodes/comfyui-kroki-wrapper/ folder
• Restart ComfyUI completely
• Check the console for any Python errors

Slow first run

• The first time you use the node, it will download and install Playwright and Chromium (~300MB)
• Subsequent runs will be much faster

Credits

• Kroki - Universal diagram rendering service
• Mermaid - Diagram syntax
• PlantUML - UML diagrams
• And all the other amazing diagram tools Kroki supports!

License

MIT License

Copyright (c) 2026

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Contributing

Issues and pull requests welcome!