Mtskheta is worth visiting year-round, but spring (April–May) and autumn (September–October) are the most pleasant. The weather is mild, the countryside is green or golden depending on the season, and the main sights are open. Summer brings more visitors — Mtskheta is an easy day trip from Tbilisi and can feel crowded at the cathedral on weekends.
Religious festivals draw large crowds of Georgian pilgrims. Mtskhetoba, the feast of the Svetitskhoveli Cathedral, is celebrated in October and is a significant national event. If you visit then, expect crowds and genuine atmosphere in equal measure.
Winter is quiet and cold, but the monuments remain open and the lack of tour groups makes for a more reflective visit. Snow on the hillsides and the cathedral is not uncommon in January and February.