Tipping norms, briefly
Tipping conventions vary a lot by country and even by service type, so there's no single "correct" percentage. In the United States, 15–20% at a sit-down restaurant is standard, with 20% common for good service and slightly less acceptable for counter service. Many other countries either build service into the price or consider a small rounding-up gesture sufficient — when traveling, it's worth checking local norms before assuming US-style tipping applies.