Why do you call these IANA time zones?

IANA maintains the tz database, the canonical list of zone identifiers such as Europe/London used by operating systems and programming languages. Naming a zone by city avoids the ambiguity of abbreviations like CST.

Do the offsets include daylight saving time?

The offsets shown are the standard (winter) offset. Many zones move forward an hour in summer for daylight saving, so the live offset can differ for part of the year.

Is the lookup done on a server?

No. The zone list is bundled with the page and all searching happens in your browser.

Time Zone List Reference

Browse IANA time zone names and their UTC offsets.

IANA time zone list

Browse the canonical IANA time zone identifiers — the Region/City names such as Asia/Tokyo and Europe/London that software uses everywhere. Search by city, region or UTC offset.

Offsets shown are the standard (winter) value; zones that observe daylight saving shift forward an hour in summer. Everything runs locally in your browser.