Tranco

Tranco is a research ranking of the top million domains. It combines several published source lists and averages them over 30 days, which is the point of it: a single day of unusual traffic cannot move a domain far, and the list is stable enough to compare with itself over time.

It was built for security research, where an unstable ranking makes results unreproducible. That origin explains its two useful properties and its one limitation.

• Reproducible. Every daily list has an identifier and stays downloadable, so a measurement can name the exact list it used.
• Manipulation-resistant. The averaging is deliberate.
• Not traffic. A Tranco rank is a popularity signal derived from other lists, not a visitor count. Nobody outside a site knows its visitor count.

What Domduck records

The tranco source, from the daily 1,000,000-line CSV rather than one lookup per domain. Each reading is stamped with the list's own end date, not the day it was downloaded, so a list built late on the 28th records ranks for the 28th.

Lower is better, and a domain outside the top million correctly gets no reading at all rather than a zero. That is the same rule as everywhere else here: a missing row means nobody could see it, and a zero would be a rank.

Reading the whole list once a day rather than each domain separately also means history exists for every tracked domain from the first day, instead of starting whenever somebody asked.

Why it matters

It is the closest thing to a working replacement for Alexa rank, and unlike the tools still selling that number, it is a list you can download and check.

Read movement rather than the absolute number. A domain going from 480,000 to 310,000 is a real change. The difference between rank 310,000 and rank 305,000 is noise, because the sources it averages disagree by more than that.