CoinLine

CoinLine is a browser extension- a simple, effective inline exchange calculator: highlight a number on any page and convert it to crypto or fiat, right where you are. No extra tab, no copy-paste into a calculator.

A passion project — something I kept wishing existed, then built.

Download Extension

Demo

coinline-demo.webm

Play Another Demo on YouTube

Features

• Click the toolbar icon to turn it ON (badge) or off again. The state is saved and restored after a browser restart.
• Select a number on a page — $1,250, €80, 0.5 BTC, and similar. A number with no currency sign is treated as USD.
• Recognizes common fiat symbols and names (USD, EUR, GBP, JPY, CAD, AUD, CHF, CNY) and crypto tickers from the live list.
• Searchable dropdown to convert into USD or any of the listed coins.
• Follows the system light or dark theme.
• Copy the converted amount to the clipboard.
• Open a TradingView chart for the selected currency pair.

Prices are refreshed when you switch the extension ON by clicking the icon.

Data

• Crypto: CoinGecko — top coins by market cap (USD).
• Fiat: ExchangeRate-API — rates vs USD.

Prices are for informational purposes only. They may not be accurate and should not be used as a decision price for any trade. Always double-check before you act.

Get in touch

Want another currency, a new feature, or just to say hi? Open an issue on github.com/janmichek/coinline.

Development

Requires Node.js. The extension build itself is a single script and does not need extra dependencies.

npm run build          # dist/chrome and dist/firefox
npm run build:chrome
npm run build:firefox

Load the built folder, not src/ or the repo root (manifest.json is written into dist/):

• Chrome: chrome://extensions → Developer mode → Load unpacked → dist/chrome
• Firefox: about:debugging#/runtime/this-firefox → Load Temporary Add-on → dist/firefox/manifest.json

After changing src/, rebuild and reload the extension. Content-script changes also need a page refresh.

Test

Chrome end-to-end tests load the unpacked dist/chrome build in Playwright's Chromium. Prices are stubbed so the suite does not call CoinGecko or ExchangeRate-API.

npm install
npx playwright install chromium
npm test

npm run test:headed    # watch the browser

Export

Store-ready zips:

npm run export           # both
npm run export:chrome    # dist/coinline-chrome.zip
npm run export:firefox   # dist/coinline-firefox.zip