About

Time Zone Guru is a small tool for answering “what’s a good time for you?” when family, friends, and colleagues are scattered across the planet.

Why it exists

Like many software teams—especially after remote work became normal—we kept talking past each other about the clock. Colleagues in Melbourne are polite about repeating that they are many hours ahead and that “today” might already be “tomorrow” for them. Doing that arithmetic by hand is a chore, and the answer changes with daylight saving.

US daylight saving does not line up with Australian rules (or European ones). A fixed “they’re +16 hours” mental model fails for weeks each year. The site always converts through real IANA zones so those transitions stay correct.

What it does

• Compare several cities on one vertical day view (mobile-friendly).
• Highlight hours where more people are likely awake.
• Optional sleep / work / awake template per local hour of day.

Data & accuracy

• Cities & zones: searchable places from GeoNames (cities roughly population ≥ 100k or each country’s largest places), plus main cities from @vvo/tzdb so smaller / remote zone labels stay findable. Each city maps to an IANA timezone id.
• Conversion & DST: the browser’s Intl.DateTimeFormat with a timeZone option (same rules engines use for formatting dates).

Offsets are never hard-coded as permanent numbers. If a government changes a rule, you pick up the fix when your browser updates. City labels refresh when we re-extract the GeoNames dump.

Built with

Static Astro site, a little TypeScript for the interactive compare tool, no heavy UI framework. Hosted as plain files for timezone.guru.