# Execution model > How the engine fills trades, orders intrabar events, and why look ahead is impossible. Source: https://docs.texttoquant.com/concepts/execution-model --- A backtest is only as trustworthy as the assumptions inside it. Every strategy, typed in plain English or assembled in the visual builder, compiles to the *same* engine, and where that engine has to make a judgment call at bar resolution, it makes the **conservative** one: ambiguous situations resolve against the trade, not in its favour. The goal is that a good result survives scrutiny, not that results look good. ## Signals, entries and exits - **Signals are evaluated on completed bars** (bar close). The engine never acts on a bar that is still forming. - **Entries are edge triggered:** a condition must become true *having been false on the previous bar* to fire. "RSI above 50" fires once when it crosses, not on every bar the condition merely stays true. - **Entry fills occur at the signal bar's close**, with configurable slippage applied against the trade direction. - **Intrabar exit ordering is conservative:** stop losses are checked before profit targets on the same bar. A bar that touches both your stop and your target books the loss. - **Fills are gap aware:** if a bar opens beyond a stop or target, the fill uses the open price, worse for a gapped stop, better for a gapped target, never the level the market skipped past. ## No look ahead The single most important guarantee: a backtest can never use information it wouldn't have had live. - **Multi timeframe and cross asset conditions read only the previous *completed* higher timeframe bar.** A 4-hour strategy consulting the daily trend sees yesterday's finished daily bar, never today's still forming one. - **Monthly bars use true calendar closes**, not fixed width approximations. - **Indicators are seeded with warm up data** before your requested start date, so a 200-period moving average is already correct on bar 1 of your window instead of spending the first months converging. The intrabar price path is unknown at bar resolution. When one bar touches both a stop and a target, the engine resolves the conflict conservatively (the stop) rather than by tick data. Backtests are hypothetical and benefit from hindsight; past performance does not guarantee future results. Related: [costs & fees](/docs/concepts/costs), [overfitting](/docs/concepts/overfitting), [robustness reference](/docs/reference/robustness).