Is 200 feet of 12-gauge extension cord safe for a tool drawing 10 amps?

Yes, it’s fine. The voltage drop is about 5%, which is within the safe range for most tools. You might notice a slight power loss under heavy load, but for light work like drills or shop vacs, you won’t feel it. Just watch out for tools with high startup surges—if they struggle, shorten the cord or go up to 10-gauge.