Your response can vary depending on the context and your relationship with the person. Here are a few options:
- Curious/Vague: "Swear what?"
- Playful: "I swear! You won't believe it!"
- Serious: "If you're asking if I can swear, I would like to think I can keep my cool."
- Casual: "Yeah, totally!"
Choose the one that fits the situation best!