Markdown Converter for Google Docs

Author: Jerry Lee
Copyright: 2026 Jerry Lee
License: MIT License
Version: 1.0

A Google Docs add-on that converts AI-generated markdown (ChatGPT, Claude, Gemini, etc.) into professionally formatted Google Docs with full support for tables, syntax-highlighted code blocks, and Mermaid diagrams.

Enjoying this tool? Buy me a coffee! Send spare change via PayPal: paypal.me/curlyman72

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Disclaimer

This 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.

Use at your own risk. Always backup your documents before running conversions.

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Features

• Complete typography support: Headers (H1-H6), bold, italic, strikethrough, inline code
• Lists: Ordered, unordered, and nested lists with proper indentation
• Tables: GitHub-flavored markdown with column alignment
• Code blocks: Syntax highlighting with monospace fonts and background colors
• Mermaid diagrams: Flowcharts, sequence diagrams, Gantt charts, class diagrams, state diagrams, and ER diagrams rendered as images
• Source code retention: Store Mermaid source in alt text, captions, or Google Doc comments
• Multiple providers: Support for mermaid.ink, MermaidChart, Kroki.io, and custom endpoints
• Source retrieval: Click any rendered diagram to view and copy its original code
• HTML entity decoding: Handles copied content from web sources

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Installation

Step 1: Open Apps Script

1. Open any Google Doc (or create a new blank document)
2. Click Extensions -> Apps Script
3. A new browser tab opens with the Apps Script editor

Step 2: Create the Main Script

1. In the Apps Script editor, you should see a file called Code.gs on the left
2. Delete any default content inside Code.gs
3. Copy and paste the contents of the Code.gs file from this repository
4. Press Ctrl+S (or Cmd+S on Mac) to save
5. Rename the project: Click "Untitled project" at the top, type "GenAI Markdown Converter", then click Rename

Step 3: Create the User Interface

1. Click the + icon next to "Files" on the left sidebar
2. Select HTML
3. Name it exactly: Sidebar (case-sensitive)
4. Delete the default HTML content
5. Copy and paste the contents of the Sidebar.html file from this repository
6. Press Ctrl+S to save

Step 4: Authorize the Script

1. Click on Code.gs to select that file and then click on Run in the menu bar
2. Google will ask for authorization:
   • Click Review Permissions
   • Choose your Google account
   • Click Advanced (if shown)
   • Click Go to {Document title || Untitled Document} (unsafe) - this is normal for custom scripts
   • Click Allow to grant document editing permissions
3. If prompted about "This app isn't verified", click Advanced then Go to...

Step 5: Test the Installation

1. Return to your Google Doc and refresh the page (F5)
2. You should see "GenAI Markdown" in the top menu bar
3. Click GenAI Markdown -> Open Converter
4. A sidebar should appear on the right side of your document

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Usage

Basic Conversion

1. Copy markdown output from your AI tool (ChatGPT, Claude, Gemini, etc.)
2. In your Google Doc, click GenAI Markdown -> Open Converter
3. Paste the markdown into the text area in the sidebar
4. Click Convert to Doc
5. Content will be inserted at your cursor position (or at the end of the document if no cursor is placed)

Configuring Settings

1. In the sidebar, click the Settings tab
2. Configure the following options:
   • Mermaid Provider: Choose between mermaid.ink (free), MermaidChart (pro), Kroki.io (free), or Custom
   • API Key: Enter your API key if using MermaidChart or a custom endpoint
   • Theme: Select diagram theme (neutral, dark, forest, base)
   • Code Retention: Choose how to store Mermaid source code:
     • Alt Text: Hidden in image metadata (right-click image -> Alt text to view)
     • Caption: Shows truncated source below the image
     • Comment: Creates a Google Doc comment with full source (requires Drive API)
     • None: Image only, no source stored
3. Click Save Settings

Retrieving Source Code

If you stored source code when converting:

1. Click on any rendered diagram in your document to select it
2. Open the GenAI Markdown sidebar
3. Click the View Source tab
4. Click Get Source from Selection
5. The original Mermaid code will appear for copying or editing

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Supported Markdown Syntax

Headers

# Heading 1
## Heading 2
### Heading 3
#### Heading 4
##### Heading 5
###### Heading 6

Typography

• **bold** or __bold__ renders as bold text
• *italic* or _italic_ renders as italic text
• ***bold italic*** renders as bold italic text
• ~~strikethrough~~ renders as strikethrough text
• `inline code` renders as inline code
• [link text](https://example.com) renders as clickable links

Lists

Unordered lists: - Item one - Item two - Nested item A - Nested item B - Item three

Ordered lists: 1. First step 2. Second step 1. Sub-step A 2. Sub-step B 3. Third step

Code Blocks

Use triple backticks with optional language identifier:

def hello_world():
    print("Hello, World!")
    return True

Tables

| Header 1 | Header 2 | Header 3 |
|:---------|:--------:|---------:|
| Left     | Center   | Right    |
| Cell A   | Cell B   | Cell C   |

Use : in the separator line for alignment:

• :--- for left align
• :---: for center align
• ---: for right align

Blockquotes

> This is a blockquote.
> It can span multiple lines.
> **Bold** and *italic* work inside blockquotes too.

Horizontal Rules

Use three or more dashes, asterisks, or underscores on their own line.

Mermaid Diagrams

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

Supported diagram types include flowcharts, sequence diagrams, Gantt charts, class diagrams, state diagrams, and ER diagrams.

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Troubleshooting

"Script Error" or "Authorization Required"

• Return to the Apps Script editor (Extensions -> Apps Script)
• Click Run -> onOpen again
• Accept all permissions that appear

Sidebar Won't Open

1. Refresh your Google Doc (F5)
2. Ensure both Code.gs and Sidebar.html are saved in Apps Script
3. Check that you ran onOpen() at least once to initialize the menu

Mermaid Diagrams Not Rendering

• Check your internet connection (diagrams render via external API)
• Try switching providers in Settings (if mermaid.ink fails, try Kroki)
• If using MermaidChart, verify your API key is valid
• Check error codes:
  • 414: Diagram too large
  • 400: Syntax error in diagram
  • 429: Rate limited

Tables or Blockquotes Formatting Incorrectly

• Ensure there are no spaces before table separator lines
• Blockquotes must start with > at the beginning of the line
• Lists cannot contain tables or blockquotes without proper spacing

Code Blocks Look Wrong

• Use standard markdown fences: three backticks on their own lines
• Language specification should be immediately after opening backticks

"Drive API Not Enabled" Error

• If using "Comment" retention mode, you must enable Drive API:
  1. In Apps Script editor, click Services (+) next to "Libraries"
  2. Select Drive API and add it
• Or switch Code Retention setting to "Alt Text" which does not require Drive API

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Security and Privacy

API Key Storage

• API keys are stored in your personal Google account via PropertiesService
• Keys are user-specific and are not shared with other document collaborators
• Keys are not transmitted to the script author or any third party except your chosen Mermaid provider
• To remove stored keys: Apps Script editor -> File -> Project Properties -> User Properties -> Delete entries

Data Processing

• Markdown content is processed locally within Google's infrastructure
• Mermaid diagrams are sent to your selected rendering service (mermaid.ink, Kroki.io, or MermaidChart)
• No document content is logged, stored, or transmitted to the script author
• Google Docs permissions are required solely to insert content into your document

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Support

If you find this tool useful, consider supporting development:

Buy me a coffee: paypal.me/curlyman72

Your support helps maintain and improve this project!

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License

MIT License

Copyright (c) 2026 Jerry Lee

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.