Building a Trading Bot Is Easy. Building a Testable Trading System Is Hard.

When building a Polymarket bot, the first version can be surprisingly small: market data ↓ strategy ↓ order That's enough to demonstrate an idea. It isn't enough to prove that the idea works. Once you care about realistic execution, the architecture becomes more interesting. Market Data ↓ Data Validation ↓ Signal Engine ↓ Risk Engine ↓ Execution Engine ↓ Trade Events ↓ Analytics This separation is what allows me to test the strategy independently from the infrastructure. 1. Don't backtest the API call One mistake I see in trading-bot development is mixing the strategy with execution. For example: if ( signal ) { await placeOrder (); } This is convenient for a prototype. But how do you test the strategy without sending an order? Instead: const signal = strategy . evaluate ( marketState ); const decision = riskEngine . check ( signal , portfolio ); if ( decision . allowed ) { await executionEngine . submit ( signal ); } Now each component can be tested independently. 2. Model execution separately A backtest shouldn't assume: signal price === fill price Instead, the execution simulator should model things such as: signal price spread slippage available liquidity fees latency Then: expected PnL ↓ execution model ↓ realistic PnL estimate The difference can be substantial. Polymarket's CLOB exposes order-book data and executable prices, making the order book an important part of any execution-aware strategy. 3. Separate in-sample and out-of-sample data Don't optimize and evaluate on the same dataset. A simple structure: Dataset ├── Train └── Test The strategy is developed using Train . Parameters are frozen. Then Test is used only for evaluation. For time-series trading, I prefer chronological splits rather than random shuffling: Past ───────────────────────> Future [ Training ][ Validation ][ Test ] This better represents the actual information flow of a trading system. 4. Measure more than win rate Win rate is useful, but insufficient. I want to measure: trades wins los