Why two brokers show different prices at the same second

[Shadow Trader]

Open the same pair on two platforms and the quotes will rarely match exactly. The difference might be a tenth of a pip or, during active moments, half a pip or more.

Each broker aggregates prices from its own set of liquidity providers, applies its own markup, and sends out ticks at its own pace. Some filter noisy ticks. Some pass through almost everything. Some add a small delay to smooth the feed.

For a scalper, this matters in two places. Signals generated on one feed and executed on another can look perfect on the chart and slightly off at the fill. And backtests built from a third-party data source can show edges that vanish on the live feed.

The best practice is to build and test strategies on the same feed they will be executed on, or at least to measure the typical difference between the signal feed and the execution feed over a few weeks.

Do you trade on the same broker that supplies your charts, or does a separate data source feed your signals?