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πŸ§œβ€β™€οΈ Mermrender

RESTful rendering pipeline for generating sequence and UML diagrams using Mermaid to embed in Github readmes, Markdown docs and more! Mermrender uses Mermaid.JS and Mermaid CLI under the hood.

Feel free to contribute by making a pull request!


Mermaid Credit:

Run Mermrender in Gitpod, a free online dev environment for GitHub:

Open in Gitpod

Hit the API! (Demo)


Setup in VSCode

Check out this awesome guide for setting up diagram rendering within VSCode:


Github doesn't support rendering Mermaid diagrams in their Markdown editor. Mermaid is a powerful tool that uses a well-defined schema to then interpret diagrams into an SVG. The idea of this tool is to allow embedding images dynamically via a REST endpoint to add UML/Sequence diagrams into your documentation/readmes/markdown files easily, whether the editor supports Mermaid or not.




1) Generate the diagram code with Mermaid OR PlantUML

    participant A as Alice
    participant J as John
    A->>J: Hello John, how are you?
    J->>A: Great!


object Object01
object Object02
object Object03
object Object04
object Object05
object Object06
object Object07
object Object08

Object01 <|-- Object02
Object03 *-- Object04
Object05 o-- "4" Object06
Object07 .. Object08 : some labels

You can edit and render them live on this website:

2) Escape the diagram to encode it

Next, you need to run it through an escaper like the following:

3) Generate the image link to embed

Send a POST request to http://localhost:3000/encode/plantuml or http://localhost:3000/encode/mermaid depending on the type with a diagram key in the body with the above escaped diagram:

Example Body:

  "diagram": "sequenceDiagram\r\n    participant Alice\r\n    participant Bob\r\n    Alice->>John: Hello John, how are you?\r\n    loop Healthcheck\r\n        John->>John: Fight against hypochondria\r\n    end\r\n    Note right of John: Rational thoughts <br/>prevail...\r\n    John-->>Alice: Great!\r\n    John->>Bob: How about you?\r\n    Bob-->>John: Jolly good!"

This will generate a respose:

  "embed_link": "http://localhost:3000/diagram/2VxdWVuY2VEaWF"

You can embed the following embed_link by using the following syntax:




<img src="http://localhost:3000/diagram/2VxdWVuY2VEaWF"/>

BBCode (Forums)


Additional Options

Add the following optional query parameters to add custom dimensions to your images:

(Not yet implemented)

How To Run

  1. npm i to install dependencies
  2. node index.js
  3. sudo npm install -g node-plantuml
  4. sudo npm install -g mermaid.cli

or run Mermrender in Gitpod, a free online dev environment for GitHub:

Open in Gitpod

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