Pachhkhaan (pachkan) is a formal vow or resolve taken before starting a fast or other austerity. It serves as the explicit agreement about what you will or will not do during the fast and helps set intention, boundaries, and accountability. It is commonly recited in the presence of a guru or at a sacred place, and it describes the exact type of upavas and the rules you will follow. In short, it codifies the practice so you stay on course.

Regarding whether it is okay to fast without pachhkhaan: traditional practice usually involves taking a pachkhaan before undertaking an upvas, as it publicly and clearly declares your discipline for that period. However, the exact custom can vary by community or tradition. Some people may begin an upvas with the intention and internal resolve even without a formal spoken pachkhaan, but many Jain communities view the pachkhaan as an important part of the vow for clarity and protection of the vow. If in doubt, consult your local guru or the temple’s guidance.

If you’d like, I can point you to more specific guidance from Jain Knowledge pages about upvas, pachkhan timings, and examples of common pachkhan texts.