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Mouse Dictionary: Super Fast Dictionary

Mouse Dictionary is a super fast dictionary for Chrome and Firefox.


  • Super fast (react in 1/60 second)
  • Awesome phrases detection
  • Capable of importing your own text data
  • Available on PDF documents!
  • Look up connected words nicely (e.g. camelCase -> camel case)
  • Customizable view

Available for various documents:


See also Getting started







Want to use for the German language? Take a look these great articles!

How to develop


Use Node.js 16+.

npm install


For Chrome:

npm run build-chrome   # Debug build
npm run release-chrome # Release build

For Firefox:

npm run build-firefox   # Debug build
npm run release-firefox # Release build

For Safari:

npm run build-safari   # Debug build
npm run release-safari # Release build

see package.json for other commands.


For the moment, Mouse Dictionary project doesn't have any strict rule about contribution. Feel free to create any issues and pull requests.

Some guides:

  • Editor: the main developer uses VSCode
  • Before you commit: try running npm run test and npm run lint

Cross-extension messaging

Mouse Dictionary supports receiving cross-extension messages. Mouse Dictionary iframe support is a good example that implements message sending to this extension.

Here is a code example for sending a message to Mouse Dictionary. You can make Mouse Dictionary look up words/expressions from other extensions.

const MD_EXTENSION_ID = "dnclbikcihnpjohihfcmmldgkjnebgnj";

chrome.runtime.sendMessage(MD_EXTENSION_ID, {
  type: "text",
  text: "rained cats and dogs",


name type value
type string must be "text"
text string text you want to look up


Mouse Dictionary is published under the MIT license.

Third-party data

This project includes some third-party data:

Dictionary data


Built-in PDF viewer

Great JavaScript libraries

See also

Chrome 拡張の高速な英語辞書ツールをつくりました(a Japanese tutorial)

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