speculari

Speculari

Speculari is a real-time market-data engine, written in Crystal, that watches order books and trade history across multiple crypto exchanges at once — Binance, Kraken, Bittrex, Braziliex, MercadoBitcoin, and NovaDax — and continuously compares them to surface arbitrage opportunities. Every second it pulls each broker's order book and recent trades, normalizes them into a shared Order model, and computes the spread between the best ask on one exchange and the best bid on another for every coin the two brokers have in common. The browser front end then lets you filter that stream by minimum spread percentage and watch discrepancies — like the 2-hour XRP gap between Kraken and MercadoBitcoin shown below — as they appear and close.

Crystal was a deliberate choice: a statically-typed, compiled language with Ruby-like syntax, chosen specifically for the concurrency (lightweight fibers via spawn) and raw throughput this workload needs — polling several exchange APIs in parallel, every few seconds, without the runtime overhead of an interpreted language.

Sample output from the arbitrage view: PDF, exported directly from the browser.