What is Unique visitor?
A unique visitor is one distinct person visiting within a period, counted once no matter how many times they return. No tool can observe a person, so every visitor count is an estimate produced by deciding which requests belong to the same someone. The method chosen determines both how accurate the number is and how much privacy it costs.
Every method is a trade
| Method | How it recognises a visitor | Cost |
|---|---|---|
| First-party cookie | An identifier stored in the browser | Needs consent in the EU and UK; cleared and blocked often |
| Fingerprinting | A profile built from device characteristics | Works without storage, and is exactly the tracking privacy law targets |
| Rotating salted hash | A daily-rotating hash of request attributes | No storage, no consent needed, and no cross-day identity |
| Logged-in identity | The account the person signed into | Precise, but only for signed-in traffic |
sonex uses the third. A visitor is recognised for the day, and when the salt rotates the identity cannot be reconstructed even by us. The deliberate cost of that: someone who visits on Monday and again on Friday counts as two visitors, because the alternative is keeping a durable identifier for a person who never agreed to one.
Why totals never match across tools
Sum daily visitors across a month and you will get a much larger number than the monthly unique count, because a person who visited eight days is counted eight times in the first and once in the second. Both are correct; they answer different questions. Any comparison of “visitors” between two tools without matching the period and the method is comparing nothing.
Ad blockers add another gap. A tool blocked for 20% of an audience reports 20% fewer visitors, and reports it confidently.
Reading it well
Treat visitor counts as a consistent index rather than a headcount. Measured the same way over time, the direction and magnitude of change are reliable even when the absolute level is not. That is enough for nearly every decision a visitor count is used for.