on the safe side

as carefully as possible in order to avoid any risk

The idiom "on the safe side" originates from the idea of erring on the side of caution, ensuring safety and avoiding unnecessary risks. It is used to describe a cautious approach or decision-making to prevent potential problems or dangers, even when the likelihood of an adverse outcome is minimal.

You probably won't need to apply for planning permission to build a shed in your garden, but to be on the safe side, check with your local planning department.
We budgeted an extra hour for the journey, just to be on the safe side in case of traffic.
The doctor prescribed a lower dosage of the medication to be on the safe side, considering potential side effects.
Before leaving for the trip, he packed an emergency kit with supplies on the safe side, in case of unforeseen situations.
When planning the event, the organizers scheduled an additional hour for setup and testing to be on the safe side and avoid any delays.