Carpenter's Tools
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The Carpenter's Tools (also known as Tools in the SNES/PS version) is a Key Item in Chrono Trigger.
In order to obtain them you need to go to the Present and talk to the carpenter in the Choras Inn and ask him for his tools. He says you can, but you need to get them from his wife. You then go back to the Midle Ages and give them to the carpenter in the tavern.