Gmail Row Highlighter

A Chrome extension that highlights Gmail message rows based on user-defined rules. You can highlight emails by sender, subject, or label criteria with custom background colors.

Features

• Flexible Rule Matching: Create rules to match emails by:
  • Sender (email address or name)
  • Subject line
  • Sender or Subject (matches if pattern appears in either field)
  • Gmail labels
• OR Pattern Matching: Use comma-separated patterns for OR logic (e.g., googledev,GDG,Google Cloud)
• Custom Colors: Choose any background color for each rule
• Edit Rules: Modify rule type, pattern, or color after creation
• Edit Colors: Click any color swatch to quickly change a rule's color
• Real-time Updates: Rules apply immediately without page reload
• Enable/Disable Rules: Toggle rules on and off without deleting them
• Privacy-Focused: All data stored locally, no external servers

Installation

Load the Extension

1. Open Chrome and navigate to chrome://extensions/
2. Enable Developer mode (toggle in the top-right corner)
3. Click "Load unpacked"
4. Select the highlight-gmail directory
5. The extension is now installed!

Usage

Creating Highlight Rules

1. Right-click the extension icon in Chrome's toolbar
2. Select "Options" (or go to chrome://extensions/ → find "Gmail Row Highlighter" → click "Options")
3. Fill out the form:
   • Rule Type: Choose from:
     • "Sender Contains" - matches sender email or name
     • "Subject Contains" - matches subject line
     • "Sender or Subject Contains" - matches if pattern appears in either field
     • "Label Contains" - matches Gmail labels
   • Pattern: Enter the text to match (e.g., @client.com, Contract:, NIAID)
     • OR Matching: Use commas to match multiple patterns (e.g., googledev,GDG,Google Cloud)
   • Background Color: Pick a color for matching emails
4. Click "Add Rule"
5. Open Gmail and see your emails highlighted!

Example Rules

• Highlight emails from a specific domain:

  • Type: Sender Contains
  • Pattern: @client.com

• Highlight emails with specific subject keywords:

  • Type: Subject Contains
  • Pattern: Contract

• Highlight emails with a specific label:

  • Type: Label Contains
  • Pattern: Important

• Highlight emails matching multiple patterns (OR logic):

  • Type: Sender or Subject Contains
  • Pattern: googledev,googlecloud@google.com,GDG,Google Developer Program
  • Matches emails containing any of these terms

Managing Rules

• Edit: Click the "Edit" button to modify a rule's type, pattern, or color
• Edit Color: Click the color swatch next to any rule to quickly change its color
• Disable/Enable: Click the "Disable" or "Enable" button next to any rule
• Delete: Click the "Delete" button to remove a rule permanently
• Rules are saved automatically - no need to click a "Save" button

How It Works

• The extension injects a content script into Gmail pages
• It observes the Gmail message list using a MutationObserver
• When new emails load or rules change, it checks each email row against your rules
• The first matching rule applies its background color to the row
• Matching is case-insensitive by default
• OR Pattern Matching: Comma-separated patterns are split and checked individually (any match triggers the rule)
• Each comma-separated term is matched as a complete phrase (e.g., "Google Cloud" matches the full phrase, not just "Google")

Technical Details

• Manifest Version: 3
• Storage: Uses Chrome's sync storage (rules sync across devices)
• Permissions: Only requires storage permission
• Privacy: All processing happens locally in your browser

Troubleshooting

Emails aren't highlighting

1. Make sure you're on mail.google.com
2. Check that your rules are enabled (not grayed out)
3. Verify the pattern matches the email content (case-insensitive)
4. Try refreshing the Gmail page

Rules not saving

1. Check Chrome's storage quota (extensions → Gmail Row Highlighter → Details)
2. Ensure you're not in incognito mode (extensions may be disabled)
3. Check the browser console for errors (F12 → Console)

Extension not working

1. Reload the extension in chrome://extensions/
2. Refresh the Gmail page
3. Check the browser console for error messages

Development

Project Structure

highlight-gmail/
├── manifest.json          # Extension configuration
├── content-script.js      # Main highlighting logic
├── styles.css             # Highlight styles
├── options.html           # Options page UI
├── options.js             # Options page logic
├── icons/                 # Extension icons
└── README.md              # This file

Building/Testing

1. Make changes to the source files
2. Go to chrome://extensions/
3. Click the refresh icon on the extension card
4. Refresh your Gmail tab to see changes

License

This project is open source. Feel free to modify and distribute.

Future Enhancements

• Regular expression pattern support
• Rule priority/ordering
• Export/import rules as JSON
• Extension popup with quick toggle
• Preset rule templates
• Case-sensitive matching option
• AND logic for multiple patterns (currently supports OR via comma-separated patterns)