Two kinds of figures are fetched from real sources.
Exchange rates refresh daily from a public rates API, and life
expectancy comes from the World Bank — male and female, latest
published year, per the country your currency implies. Both live in
the site's own database and arrive with an "as of" date; a baked-in
snapshot covers total failure, and Taiwan stays hand-estimated
because the World Bank doesn't publish it.
Everything else was written by hand by the author —
informed estimates, not retrieved from any dataset. That varies in
reliability. Population, temperatures and climate classifications are
well-documented facts. Cost of living is an estimate, and it's the number
that drives every result — each city's popup shows the date its figures
were last hand-checked. The safety, English, internet and transport
scores are coarse judgements on a 0–100 scale; real published indices
exist for several of them, but they were not used, so the car-free score
is not a Walk Score despite resembling one.
Visa and tax entries are the most perishable thing here.
Thailand's remittance rules changed in 2024, Portugal's NHR regime closed
to new entrants, and Indonesia's treatment of foreign income has moved more
than once. Treat them as a prompt to go and check, never as an answer.
The honest summary: the ranking between cities is far more
trustworthy than any individual number's apparent precision.