A backtesting tool is a research instrument, and like any instrument it is judged by what it refuses to hide. Before you pay for one, find out how it handles costs, out-of-sample testing, and the boring details of data — those three questions eliminate most of the field.
Execution realism comes before feature count
The fastest way to ruin a backtest is to assume every order fills at the close price with no friction. Spreadsheet tests and entry-level tools quietly do exactly that. Serious software models the spread, the commission, and the slippage you would actually pay, and lets you set those assumptions per instrument rather than hiding them behind a default. Ask a vendor how fills are modeled and whether you can see the cost profile the test used — if the answer is a marketing page, keep looking.
The second question is about time. A strategy that is tuned and scored on the same history is being graded on its own homework. Look for walk-forward testing, a holdout that the tuning process never touches, and statistics that correct for how many variations you tried. These features are what separate a measurement from a story.
A short evaluation checklist
That last row matters more than it looks. Most backtests end as a CSV nobody acts on. Tools where a passing test becomes a paper run in the same system close the gap between research and behavior — which is the entire point of testing in the first place.