Tick data is not free, even when the download is

[Fairman]

Tick data is not free, even when the download is

Downloading years of tick data for a major pair is easy. Trusting it is another matter.

Gaps are common. A feed that dropped for a few minutes leaves holes, and a backtest simply jumps across them. Some sources fill the gap with synthetic ticks, which look like data but are invented.

Timestamps can be off. A source that records time in local time instead of UTC, or shifts at daylight saving changes, misaligns events with the news calendar.

Spreads may be missing or fixed. Some free datasets hold only bid prices, leaving the ask to be guessed with a constant spread that never existed.

Volume is usually the number of quotes, which may differ widely between providers.

The fix is checking. Compare the dataset with another source for a few known events, such as a major data release or a known spike, and look at whether the sequences match. Then count the gaps and check the timestamps around daylight saving.

A clean approach is building a small checklist: timestamps in UTC, no gaps over a set length, spreads present and varying, no negative spreads, no jumps beyond a threshold. Any dataset passing all five earns a measure of trust.

What checks have been run on tick data before trusting a test built on it?