Here is a frugal tip that I found works great to clean the glass on a woodstove. This is a natural and free way to clean your woodstove door glass.
First make sure the glass is cold or at least just warm. Wet some newspaper and add some ash from your woodstove to the paper. Use the damp newspaper with the ash to wipe off the inside of the glass. The wood ash acts as effective paste to clean off the glass. If you have some stubborn soot buildup just continue to scrub with the paste until it comes off. It does make a bit of a mess on the glass and a lot of elbow grease if you have a hard soot buildup to clean off.
Once you have the glass cleared of soot, let it dry. Then use a dry paper towel or rag to wipe off the glass for a final clean up of the woodstove door.