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Real-time arbitrage scanner between Polymarket and Kalshi prediction markets Stop flipping between tabs to compare prediction market odds. Start seeing the spread instantly. If you trade on Polymarket, you've probably wondered whether the same event is priced differently on Kalshi. Maybe you've opened both sites, found the same market, compared the numbers, and tried to do the math in your head. By the time you finish, the prices have already moved. Cross-market arbitrage exists in prediction markets, but catching it manually is slow, tedious, and error-prone. That gap between platforms is where money hides. WHY CROSS-MARKET ARBITRAGE IS SO HARD TO CATCH Polymarket and Kalshi are the two largest prediction markets, but they operate independently. Each has its own user base, its own liquidity, and its own price discovery. That means the same real-world event can be priced differently on each platform at the same time. The problem is finding those differences before they vanish: - Different naming conventions make it hard to even find the same event on both platforms - Price formats differ — Polymarket shows probabilities, Kalshi shows cent-denominated contracts - Odds shift constantly — a 3% spread can close in seconds - Manual comparison requires multiple tabs, mental math, and constant refreshing - There's no single dashboard that overlays both platforms side by side Most traders just eyeball it. Some use spreadsheets. Both approaches are too slow for a market that moves in real time. This extension puts both sides of the trade in one view, calculates the spread for you, and tells you exactly where the arbitrage is. WHAT THIS EXTENSION DOES PolyArbitrage is a side panel tool that runs alongside your Polymarket browsing. When you visit a Polymarket event page, it automatically searches for the matching event on Kalshi, pulls live pricing from both platforms, and calculates whether an arbitrage opportunity exists. No spreadsheets. No second browser window. No manual lookups. Here's what you get: Automatic Event Matching — Navigate to any Polymarket event page. The extension extracts the event title, searches Kalshi's open markets using intelligent keyword matching, and links them together. Matched events are cached for 24 hours so repeat visits load instantly. Live Odds Comparison — Side-by-side display of YES and NO prices from both Polymarket and Kalshi, normalized to the same format. Updated every 4-12 seconds depending on how close the spread is to breakeven. Spread Analysis — Two-directional spread calculation. Direction 1: Buy YES on Polymarket + Buy NO on Kalshi. Direction 2: Buy NO on Polymarket + Buy YES on Kalshi. Each direction shows total cost and profit percentage. A green badge appears when a positive arbitrage exists. Arbitrage Calculator — When the extension detects a profitable spread, a calculator panel appears. Enter your bankroll, and it shows the optimal allocation across both platforms, your guaranteed payout, and your net profit. The math updates in real time as you adjust the amount. Adaptive Polling — When prices are near breakeven (within 3% of arbitrage), the extension polls every 4 seconds to catch fleeting opportunities. When the spread is wide, it relaxes to 12-second intervals to reduce API load. HOW IT WORKS 1. Install the extension and navigate to any event page on polymarket.com 2. Click the extension icon to open the side panel 3. The scanner automatically detects the event and searches for a Kalshi match 4. If matched, live odds from both platforms appear side by side 5. Spread analysis shows whether arbitrage exists in either direction 6. If profitable, the calculator shows exactly how to allocate your capital That's it. The entire workflow happens without leaving the Polymarket page. WHY A SIDE PANEL Most Chrome extensions use popups. Popups disappear the moment you click anywhere else on the page. For a tool that needs to stay visible while you browse, read market rules, and place trades, that's a dealbreaker. The side panel stays pinned alongside the main page. You can scroll through Polymarket, read comments, check the order book — and the arbitrage scanner remains visible the whole time. It's the difference between glancing at a dashboard and repeatedly opening a drawer. SMART EVENT MATCHING Finding the same event across platforms is harder than it sounds. Polymarket might call it "Will Trump be impeached by end of 2026?" while Kalshi lists it as "Will President Trump be impeached during his term?" Same event, different words. The extension handles this by extracting meaningful keywords from the Polymarket title — filtering out common words like "will," "the," and "be" — then scoring every open Kalshi event against those keywords. The best match above a confidence threshold gets selected. Results are cached locally so the same event loads instantly on repeat visits. If no match is found, the extension says so clearly. No false matches, no guessing. REAL SCENARIOS WHERE THIS HELPS Spotting a quick arb: You're browsing a political event on Polymarket. YES is trading at 12.5 cents. You open the side panel and see Kalshi has YES at 10.0 cents. The spread analysis shows PM NO + Kalshi YES costs 97.5 cents per dollar of payout — a 2.6% guaranteed return. You enter $1,000 in the calculator: $897 on Polymarket NO, $103 on Kalshi YES, guaranteed payout $1,025.64. Monitoring a narrowing spread: An event that was 5% apart yesterday is now at 1.8%. The extension is polling every 4 seconds because the spread is near breakeven. You watch the numbers in the side panel while deciding whether to close your position. Validating a price before trading: You see an event at 13% on Polymarket and wonder if the market is efficient. A glance at the side panel shows Kalshi has the same event at 10%. The 3% gap might reflect different market dynamics, or it might be a pricing error worth exploiting. Scanning across multiple events: You navigate from event to event on Polymarket. Each time, the side panel automatically searches Kalshi and updates. No need to manually look up each event — just browse normally and let the scanner do its job. Checking market efficiency: You're researching whether prediction markets are well-calibrated. By visiting various events, you can quickly see which ones have significant cross-platform spreads and which ones are tightly aligned. Running the numbers before committing: You found an opportunity but want to see the exact allocation. Enter different bankroll amounts in the calculator — $500, $1,000, $5,000 — and see how net profit scales. The guaranteed payout calculation helps you decide if the return is worth the effort of placing two separate trades. WHAT THIS EXTENSION DOES NOT DO This extension does not execute trades. It does not access your account on either platform. It does not store any personal information. It does not scrape or modify the Polymarket page in any way beyond reading the URL to detect which event you are viewing. All data is fetched from public APIs: - Polymarket odds from the Gamma API (gamma-api.polymarket.com) - Kalshi odds from the Kalshi public API (api.elections.kalshi.com) The only permissions it uses: - storage — Caches event matches locally for 24 hours so repeat visits don't re-search Kalshi. Nothing leaves your browser. - sidePanel — Displays the scanner in Chrome's built-in side panel. - Host permissions for polymarket.com — Content script detects which event page you're viewing. - Host permissions for gamma-api.polymarket.com and api.elections.kalshi.com — Fetches live pricing data from both platforms. No analytics. No tracking. No third-party services. Everything runs locally in your browser. THE MATH BEHIND THE SPREAD The arbitrage calculation is straightforward: Direction 1: Buy YES on Polymarket + Buy NO on Kalshi Total cost = PM YES price + Kalshi NO price Profit = $1.00 - total cost Direction 2: Buy NO on Polymarket + Buy YES on Kalshi Total cost = PM NO price + Kalshi YES price Profit = $1.00 - total cost If either direction costs less than $1.00, you have a guaranteed profit regardless of the outcome. The calculator allocates your bankroll proportionally across the two positions to maximize the guaranteed payout. No hidden logic. No rounding tricks. The same formula runs on every update cycle. WHO THIS IS FOR - Prediction market traders who use both Polymarket and Kalshi and want to spot mispricings - Arbitrage hunters looking for cross-platform opportunities without manual comparison - Quantitative bettors who want real-time spread data while browsing events - Market researchers studying price efficiency across competing prediction platforms - Anyone curious about whether the odds they see on one platform are fair relative to another GETTING STARTED Install the extension, visit any event on polymarket.com, and click the icon. The side panel opens, the scanner runs, and you see the result in seconds. No account needed. No sign-up. No configuration. Just browse and scan.