There are two ways to get this data, and the user experience varies wildly.
In the world of algorithmic and retail trading, the phrase "garbage in, garbage out" is the ultimate commandment. The quality of your backtest is only as good as the data you feed into your strategy. For serious traders—whether you are a quantitative hedge fund manager or a dedicated retail Forex scalper—one name consistently rises to the top when discussing tick-by-tick accuracy: . dukascopy+historical+data