A blackjack basic-strategy overlay for the browser.
Real-time Hit / Stand / Double / Split guidance with live probabilities.
Emerald is a lightweight Chrome (Manifest V3) extension that displays a draggable, on-screen overlay while you play blackjack. For any combination of your hand and the dealer's up-card, it shows the mathematically optimal basic-strategy decision and the underlying win, push, and bust probabilities — so you can see not just what to do, but why.
The strategy engine is a faithful implementation of a standard basic-strategy chart, covering hard totals, soft totals, and pairs.
- Floating, draggable overlay that sits on top of any online blackjack table. It loads automatically on duel.com and can be toggled from the toolbar icon anywhere else.
- Instant recommendations derived from the built-in basic-strategy chart (hard totals, soft totals, and pairs).
- Fast manual entry — one click to set the dealer's up-card, one click per card in your hand.
- Live probabilities computed with an infinite-deck model:
- Probability the dealer busts
- Probability of winning or pushing if you stand
- Probability of busting if you hit
- Automatic blackjack and bust detection.
- Emerald dark theme with chart-matching color codes: green (Hit), blue (Double), red (Stand), gray (Split).
- Clone the repository:
git clone https://github.com/vskstudio/Emerald.git
- Open
chrome://extensionsin Chrome, Edge, or Brave. - Enable Developer mode (top-right toggle).
- Click Load unpacked and select the
Emeralddirectory.
- Open your online blackjack table.
- Click the Emerald toolbar icon to reveal the overlay (it appears automatically on duel.com).
- Select the dealer's up-card.
- Add your cards — the recommendation and probabilities update instantly with each click.
- Use New deal to reset between hands.
The decision logic is implemented in src/strategy.js and recommends one of four actions, color-coded in the overlay:
| Action | Color |
|---|---|
| Hit | 🟩 Green |
| Double | 🟦 Blue |
| Stand | 🟥 Red |
| Split | ⬜ Gray |
| Path | Purpose |
|---|---|
manifest.json |
Extension manifest (Manifest V3) |
src/strategy.js |
Basic-strategy chart and probability calculations |
src/content.js |
Overlay UI and interaction logic |
src/background.js |
Service worker handling toolbar-triggered injection |
src/overlay.css |
Overlay styling |
icons/ |
Extension and overlay icons |
Emerald is provided for educational purposes only. Basic strategy reduces the house edge but does not guarantee winnings. Please gamble responsibly.
Released under the MIT License.
Made with 💚 by VSK Studio