Matching Prediction Markets Across Venues Is Harder Than It Looks
A developer building a cross-venue price comparison tool for prediction markets found that the biggest challenge was not aggregating order books but determining whether two markets on different platforms refer to the same event. Platforms like Polymarket and Kalshi use entirely different naming conventions, slugs, and ticker formats, making automated matching unreliable — for example, a fuzzy title match on a Fed rate decision can accidentally pair five separate Fed meeting markets. Even within a single venue, the same question can appear as two distinct listings with unrelated identifiers, falsely signaling arbitrage opportunities to any matcher that assumes internal uniqueness. The developer identified resolution date, resolution source, outcome buckets, and settlement rules as the most discriminating factors for accurate matching, with price comparison coming last. Both Polymarket and Kalshi offer read-only public APIs without requiring authentication, and the developer published a full reference guide along with a live matching terminal called Preduck covering data from September 13, 2026.
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