Automotive window tint is damaged by ammonia, which happens to be a very common component of household window cleaners (including Windex!). Ammonia will make the tint weaker to UV radiation contained in sunlight. Continued use can leave your tint purple and bubbled.
Automotive window cleaners are made with no ammonia, and are 100% safe for tint. Two brands we specifically recommend are Stoner's Invisible Glass and Sprayway Glass Cleaner. Both are available locally at Walmart, Home Depot, and other major retail chains.
NOTE: Some vehicles that come stock with tinted windows tint the actual glass, rather than applying a tinted film. Ammonia-based cleaners can normally be used safely on these windows, but it's best to be safe unless you're 100% sure your tint is compatible with ammonia!