UniRate Currency Converter — browser extension

A tiny, zero-dependency browser extension that puts live currency conversion in your toolbar. Convert any amount between 170+ currencies, look up exchange rates, and check VAT rates — powered by the free UniRate API.

Works on Firefox, Chrome, and Edge (Manifest V3).

• 💱 Convert amounts between any supported currencies
• 📈 Live exchange rates from unirateapi.com
• 🧾 VAT-rate lookups
• 🌓 Light & dark mode, matches your system
• 🔒 Your API key never leaves your browser except to call api.unirateapi.com
• 📦 No runtime dependencies — vanilla HTML/CSS/JS, no build step, no bundler

Install

Store listings (self-serve, free):

• Firefox — Add-ons (AMO)
• Chrome — Chrome Web Store
• Edge — Edge Add-ons

Store links are added as each listing goes live.

Manual / development install

The extension is plain static files — no build required.

• Firefox: about:debugging → This Firefox → Load Temporary Add-on → pick manifest.json.
• Chrome / Edge: chrome://extensions → enable Developer mode → Load unpacked → select this folder.

Setup

1. Get a free API key at unirateapi.com.
2. Open the extension's Settings (the ⚙ button in the popup, or the extension's options page) and paste your key.
3. Open the popup, pick your currencies, and convert.

Your key and preferences are stored with the browser's storage.local API — local to your browser. The only network requests the extension makes are GET calls to https://api.unirateapi.com.

How it works

All API logic lives in src/unirate.js — a dependency-free client with an injectable fetch, so it is unit-tested entirely offline and shared between the popup and the Node tests/example. It implements the four free-tier endpoints the UI needs:

Method	Endpoint	Returns
getRate(from, to?)	/api/rates	one rate, or a map of all rates
convert(to, amount?, from?)	/api/convert	converted amount
getSupportedCurrencies()	/api/currencies	list of currency codes
getVATRates(country?)	/api/vat/rates	one country's VAT data, or all

The Pro-gated historical/timeseries endpoints are intentionally not included, so the extension can never surface a 403 to an end user.

import { UniRateClient } from "./src/unirate.js";

const client = new UniRateClient({ apiKey: "your-key" });
const eur = await client.convert("EUR", 100, "USD"); // 100 USD → EUR

Error handling

Every failure is a UniRateError carrying a statusCode: 401 (bad key), 404 (unknown currency), 429 (rate limited), 503 (service unavailable), and a wrapped transport error for network problems.

Development

# Run the mock test suite (Node stdlib only, no install, fully offline)
node --test

# Run the live free-tier tests against the real API
UNIRATE_API_KEY=your-key node --test

# Try the client from Node
UNIRATE_API_KEY=your-key node examples/node-example.mjs

# Regenerate the PNG icons from pure math (zlib only)
node tools/make-icons.mjs

# Lint the extension with Mozilla's web-ext (dev-only tool, fetched on demand)
npx web-ext lint --source-dir .

Per this project's container-isolation policy, run the npx/node commands inside the dev node sandbox rather than on the host.

Related UniRate clients

Official UniRate clients exist for Python, Node, Go, Rust, Java, Ruby, PHP, .NET, Swift, Elixir, Perl, R, and more — see github.com/UniRate-API.

License

MIT © 2026 Unirate Team. See LICENSE.