RateAlert — Real-Time Currency Tracker

A trading-terminal-styled currency tracker: pick a pair, watch a live sparkline build tick by tick, and arm a threshold so you're notified the moment a rate crosses the level you care about.

Live demo →

Features

• Live polling (every 15 seconds) of any supported currency pair while the tab is open
• Rolling sparkline chart of the last 40 ticks, rendered in plain SVG — no chart library
• Threshold alerts ("notify me when USD/PHP goes above 58.50") with an in-page log and an optional browser Notification
• Terminal-style UI: monospace type, amber ticker display, up/down deltas
• Handles the real edge cases of a public API: unreachable rates and permission-denied notifications, each with a clear fallback
• Zero dependencies — vanilla HTML, CSS, and JavaScript

Why no backend?

open.er-api.com serves live exchange rates over plain HTTPS with CORS enabled, so the browser can poll it directly — no server needed to proxy requests or hide a key, because none is required.

The trade-off: this is a static, client-only app, so polling and alerts only run while the browser tab is open. A production version would need a small backend or scheduled worker to keep watching and push alerts once the tab is closed.

Note on tick freshness: the free rate API updates roughly hourly upstream, so ticks may repeat the same value between upstream refreshes even though the app polls every 15 seconds — that's expected, not a bug.

Run it locally

Clone the repo and open index.html in a browser. No build step, no npm install.

git clone https://github.com/arjayb/RateAlert.git
cd RateAlert
open index.html # or just double-click it

If your browser blocks fetch on the file:// protocol, serve it with any static server instead:

python3 -m http.server 8000
# then visit http://localhost:8000

Deploy to GitHub Pages

1. Push this repo to GitHub.
2. Go to Settings → Pages.
3. Under Build and deployment, set Source to Deploy from a branch, pick main and / (root).
4. Save — your app will be live at https://<your-username>.github.io/RateAlert/ within a minute or two.

Project structure

RateAlert/
├── index.html # markup
├── style.css # CRT terminal theme, ticker, sparkline layout
├── script.js # polling loop, sparkline rendering, threshold + notification logic
└── README.md

Data source

All rates come from open.er-api.com, a free, keyless exchange-rate API. No authentication, no API key, no user data is stored — every tick is a fresh, live request. Alerts are checked entirely client-side against the latest tick.

License

MIT — use this however you'd like.